Difference between revisions of "2005 AIME II Problems/Problem 14"

Latest revision as of 15:38, 21 August 2024

1 Problem
2 Solution 1
3 Solution 2 (Similar Triangles)
4 Solution 3 (LoC and LoS bash)
5 Solution 4 (Ratio Lemma and Angle Bisector Theorem)
6 Solution 5 (Isogonal lines with respect to A angle bisesector)
7 Solution 6 (Tangent subtraction formulas)
8 Solution 8 (Isogonal Conjugates)
9 Solution 9 (Short and no IQ Required Altogether-Bash)
10 Solution 10
11 Solution 11 (Ultimate Stewarts Bash)
12 See also

Problem

In triangle $ABC, AB=13, BC=15,$ and $CA = 14.$ Point $D$ is on $\overline{BC}$ with $CD=6.$ Point $E$ is on $\overline{BC}$ such that $\angle BAE\cong \angle CAD.$ Given that $BE=\frac pq$ where $p$ and $q$ are relatively prime positive integers, find $q.$

Solution 1

$[asy] import olympiad; import cse5; import geometry; size(150); defaultpen(fontsize(10pt)); defaultpen(0.8); dotfactor = 4; pair A = origin; pair C = rotate(15,A)*(A+dir(-50)); pair B = rotate(15,A)*(A+dir(-130)); pair D = extension(A,A+dir(-68),B,C); pair E = extension(A,A+dir(-82),B,C); label("$A$",A,N); label("$B$",B,SW); label("$D$",D,SE); label("$E$",E,S); label("$C$",C,SE); draw(A--B--C--cycle); draw(A--E); draw(A--D); draw(anglemark(B,A,E,5)); draw(anglemark(D,A,C,5)); [/asy]$

By the Law of Sines and since $\angle BAE = \angle CAD, \angle BAD = \angle CAE$ , we have

$\begin{align*} \frac{CD \cdot CE}{AC^2} &= \frac{\sin CAD}{\sin ADC} \cdot \frac{\sin CAE}{\sin AEC} \\ &= \frac{\sin BAE \sin BAD}{\sin ADB \sin AEB} \\ &= \frac{\sin BAE}{\sin AEB} \cdot \frac{\sin BAD}{\sin ADB}\\ &= \frac{BE \cdot BD}{AB^2} \end{align*}$

Substituting our knowns, we have $\frac{CE}{BE} = \frac{3 \cdot 14^2}{2 \cdot 13^2} = \frac{BC - BE}{BE} = \frac{15}{BE} - 1 \Longrightarrow BE = \frac{13^2 \cdot 15}{463}$ . The answer is $q = \boxed{463}$ .

Solution 2 (Similar Triangles)

Drop the altitude from A and call the base of the altitude Q. Also, drop the altitudes from E and D to AB and AC respectively. Call the feet of the altitudes R and S respectively.

From here, we can use Heron's Formula to find the altitude. The area of the triangle is $\sqrt{21*6*7*8} = 84$ . We can then use similar triangles with triangle $AQC$ and triangle $DSC$ to find $DS=\frac{24}{5}$ . Consequently, from Pythagorean theorem, $SC = \frac{18}{5}$ and $AS = 14-SC = \frac{52}{5}$ . We can also use the Pythagorean theorem on triangle $AQB$ to determine that $BQ = \frac{33}{5}$ .

Label $AR$ as $y$ and $RE$ as $x$ . $RB$ then equals $13-y$ . Then, we have two similar triangles.

Firstly: $\triangle ARE \sim \triangle ASD$ . From there, we have $\frac{x}{y} = \frac{\frac{24}{5}}{\frac{53}{5}}$ .

Next: $\triangle BRE \sim \triangle BQA$ . From there, we have $\frac{x}{13-y} = \frac{\frac{56}{5}}{\frac{33}{5}}$ .

Solve the system to get $x = \frac{2184}{463}$ and $y = \frac{4732}{463}$ . Notice that 463 is prime, so even though we use the Pythagorean theorem on $x$ and $13-y$ , the denominator won't change. The answer we desire is $\boxed{463}$ .

Solution 3 (LoC and LoS bash)

Let $\angle CAD = \angle BAE = \theta$ . Note by Law of Sines on $\triangle BEA$ we have $\frac{BE}{\sin{\theta}} = \frac{AE}{\sin{B}} = \frac{AB}{\sin{\angle BEA}}$ As a result, our goal is to find $\sin{\angle BEA}$ and $\sin{\theta}$ (we already know $AB$ ).

Let the foot of the altitude from $A$ to $BC$ be $H$ . By law of cosines on $\triangle ABC$ we have $169 = 196 + 225 - 2 \cdot 14 \cdot 15 \cdot \cos{C} \Rightarrow \cos{C} = \frac{3}{5}$ It follows that $AH = \frac{56}{5}$ and $HC = \frac{42}{5} \Rightarrow HD = \frac{12}{5}$ .

Note that by PT on $\triangle AHD$ we have that $AD^2 = \left(\frac{56}{5}\right)^2 + \left(\frac{12}{5}\right)^2 = \frac{656}{5}$ . By Law of Sines on $\triangle ADC$ (where we square everything to avoid taking the square root) we see $\frac{36}{\sin^2{\theta}} = \frac{656}{5 \cdot \frac{16}{25}} \Rightarrow \sin^2{\theta} = \frac{36}{205}.$ How are we going to find $\sin{\angle BEA}$ though? $\angle BEA$ and $\theta$ are in the same triangle. Applying Law of Sines on $\triangle ABC$ we see that $\frac{13}{\frac{4}{5}} = \frac{14}{\sin{\angle B}} \Rightarrow \sin{\angle B} = \frac{56}{65} \Rightarrow \cos{\angle B} = \frac{33}{65}.$ $\theta$ , $\angle B$ , and $\angle BEA$ are all in the same triangle. We know they add up to $180^{\circ}$ . There's a good chance we can exploit this using the identity $\sin{p} = \sin{180^{\circ}-p}$ .

We have that $\sin{(180^{\circ} - (\theta + \angle B))} = \sin{\angle BEA} = \sin{(\theta + \angle B)}$ . Success! We know $\sin{\theta}$ and $\sin{\angle B}$ already. Applying the $\sin$ addition formula we see $\sin{\theta + \angle B} = \sin{\theta} \cos{\angle B} + \sin{\angle B} \cos{\theta} = \frac{6}{\sqrt{205}} \cdot \frac{33}{65} + \frac{56}{65} \cdot \frac{13}{\sqrt{205}}=\frac{1}{65 \cdot \sqrt{205}} (198 + 728) = \frac{926}{65 \sqrt{205}}.$ This is the last stretch! Applying Law of Sines a final time on $\triangle BEA$ we see $\frac{BE}{\sin{\theta}} = \frac{13}{\sin{BEA}} \Rightarrow \frac{BE}{\frac{6}{\sqrt{205}}} = \frac{13}{\frac{926}{65\sqrt{205}}} \Rightarrow \frac{BE}{6} = \frac{13 \cdot 65}{926} \Rightarrow \frac{13 \cdot 65 \cdot 6}{926} = BE = \frac{2535}{463}.$ It follows that the answer is $\boxed{463}$ .

Solution 4 (Ratio Lemma and Angle Bisector Theorem)

Let $AK$ be the angle bisector of $\angle A$ such that $K$ is on $BC$ .

Then $\angle KAB = \angle KAC$ , and thus $\angle KAE = \angle KAD$ .

By the Ratio Lemma, $\frac{BE}{KE} = \frac{BA}{KA} * \frac{\sin{BAE}}{\sin{KAE}}$ and $\frac{CD}{KD} = \frac{CA}{KA} * \frac{\sin{CAD}}{\sin{KAD}}$ .

This implies that $\frac{BE}{KE*BA} = \frac{CD}{KD*CA}$ .

Thus, $\frac{BE}{KE} = \frac{13}{14} * \frac{6}{DK}$ .

$DK = CK - 6 = 14*15/27 - 6 = 16/9$ . Thus, $\frac{BE}{KE} = \frac{13*54}{14*16}$ .

Additionally, $BE + KE = 13*15/27 = 65/9$ . Solving gives that $q = 463.$

Alternate: By the ratio lemma, $BD/DC = (13/14)*(\sin BAD/\sin DAC)$ $EC/EB = (14/13)*(\sin EAC/\sin BAE)$

Combining these, we get $(BD/DC)(14/13) = (EC/EB)(13/14)$ $(3/2)(14/13)(14/13) = (15-x)(x)$

$x = 2535/463$ Thus, $q = 463$

Solution 5 (Isogonal lines with respect to A angle bisesector)

Since $AE$ and $AD$ are isogonal with respect to the $A$ angle bisector, we have $\frac{BE}{EC}\cdot \frac{BD}{DC}=(\frac{AB}{AC})^2.$ To prove this, let $\angle BAE=\angle DAC=x$ and $\angle BAD=\angle CAE=y.$ Then, by the Ratio Lemma, we have $\frac{BD}{DC}=\frac{AB\sin y}{AC\sin x}$ $\frac{BE}{EC}=\frac{AB\sin x}{AC\sin y}$ and multiplying these together proves the formula for isogonal lines. Hence, we have $\frac{BE}{15-BE}\cdot \frac{9}{6}=\frac{169}{196}\implies BE=\frac{2535}{463}$ so our desired answer is $\boxed{463}.$

Solution 6 (Tangent subtraction formulas)

Note: We first recall some helpful tips regarding 13, 14, 15 triangles. Drawing an altitude H from B to AC results in AHB being a 5-12-13 right triangle and CHB being a 3-4-5 (9-12-15) right triangle.

$[asy] import olympiad; import cse5; import geometry; size(300); defaultpen(fontsize(10pt)); defaultpen(0.8); dotfactor = 4; pair A = origin; pair C = rotate(15,A)*(A+dir(-50)); pair B = rotate(15,A)*(A+dir(-130)); pair D = extension(A,A+dir(-68),B,C); pair E = extension(A,A+dir(-82),B,C); label("$A$",A,N); label("$B$",B,SW); label("$D$",D,SE); label("$E$",E,S); label("$C$",C,SE); draw(A--B--C--cycle); draw(A--E); draw(A--D); draw(anglemark(B,A,E,5)); draw(anglemark(D,A,C,5)); pair G = foot(E,C,A); pair F = foot(D,C,A); draw(D--F); draw(E--G); label("$G$",G,N); label("$F$",F,N); [/asy]$

Now we start by drawing altitudes from D and E onto AC, labeling them as F and G, and labelling $\angle DAG = \alpha$ . Now we know that $\overline{DF} = \frac{24}{5}$ and $\overline{FC} = \frac{18}{5}$ . Therefore, $\overline{AF} = \frac{52}{5}$ , so $\tan{(\alpha)} = \frac{6}{13}$ . Our goal now is to use tangent $\angle EAG$ in triangle $AEG$ . We set $\overline{BE}$ to $x$ , so $\overline{ED} = 9 - x$ and $\overline{EC} = 15 - x$ , so $\overline{EG} = \frac{4}{5}(15-x)$ and $\overline{GC} = \frac{3}{5}(15-x)$ so $\overline{AG} = \frac{3x+25}{5}$ . Now we just need tangent of $\angle EAG$ .

We find this using $\tan{(EAG)} = \tan{(A - \alpha)} = \frac{\tan{A} - \tan{\alpha}}{1 + \tan{A}\tan{\alpha}}$ , which is $\frac{\frac{12}{5} - \frac{6}{13}}{1 + \frac{12}{5} \cdot \frac{6}{13}}$ or $\frac{126}{137}$ . Now we solve the equation $\tan{\angle EAG} = \frac{126}{137} = \frac{\frac{60-4x}{5}}{\frac{3x+25}{5}}$ , so $x = \frac{2535}{463}$

Solution 8 (Isogonal Conjugates)

Let $ED = x$ , such that $BE = 9-x$ . Since $\overline{AE}$ and $\overline{AD}$ are isogonal, we get $\frac{9-x}{6+x} \cdot \frac{9}{6} = \frac{13^2}{14^2} \Rightarrow 588(9 - x) = 338(6 + x)$ , and we can solve to get $x = \frac{1632}{463}$ (and $BE = \frac{2535}{463}$ ). Hence, our answer is $\boxed{463}$ . - Spacesam

Solution 9 (Short and no IQ Required Altogether-Bash)

Diagram borrowed from Solution 1.

$[asy] import olympiad; import cse5; import geometry; size(150); defaultpen(fontsize(10pt)); defaultpen(0.8); dotfactor = 4; pair A = origin; pair C = rotate(15,A)*(A+dir(-50)); pair B = rotate(15,A)*(A+dir(-130)); pair D = extension(A,A+dir(-68),B,C); pair E = extension(A,A+dir(-82),B,C); label("$A$",A,N); label("$B$",B,SW); label("$D$",D,SE); label("$E$",E,S); label("$C$",C,SE); draw(A--B--C--cycle); draw(A--E); draw(A--D); draw(anglemark(B,A,E,5)); draw(anglemark(D,A,C,5)); [/asy]$

Applying Law of Cosines on $\bigtriangleup ABC$ with respect to $\angle C$ we have $AB^2=AC^2+BC^2-2(AC)(BC)\cos C$ Solving gets $\cos C=\frac{3}{5}$ , which implies that $\sin C=\sqrt{1-\cos C}=\frac{4}{5}$ Applying Stewart's Theorem with cevian $AD$ we have $(BC)(AD)^2+(BC)(BD)(CD)=(CD)(AB)^2+(BD)(AC)^2$ Solving gets $AD=\frac{4\sqrt{205}}{5}$ .

Applying Law of Sines on $\bigtriangleup ACD$ to solve for $\sin CAD$ we have $\frac{AD}{\sin C}=\frac{CD}{\sin CAD}$ Solving gets $\sin CAD=\frac{6\sqrt{205}}{205}$ . Thus $\sin BAE=\sin CAD=\frac{6\sqrt{205}}{205}$ .

Applying Law of Sines on $\bigtriangleup ABC$ we have $\frac{AC}{\sin B}=\frac{AB}{\sin C}$ Solving gets $\sin B=\frac{56}{65}$ .

Applying Stewart's Theorem with cevian $AE$ we have $(BC)(AE)^2+(BC)(BE)(CE)=(CE)(AB)^2+(BE)(AC)^2$ $(BC)(AE)^2+(BC)(BE)(BC-BE)=(BC-BE)(AB)^2+(BE)(AC)^2$ Solving gets $AE=\sqrt{\frac{15BE^2-198BE+2535}{15}}$

Finally, applying Law of Sines on $\bigtriangleup BAE$ we have $\frac{AE}{\sin B}=\frac{BE}{\sin BAE}$ $\frac{\sqrt{\frac{15BE^2-198BE+2535}{15}}}{\frac{56}{65}}=\frac{BE}{\frac{6\sqrt{205}}{205}}$ $7605BE^2-32342BE+2535=0$ Solving the easy quadratic equation gets $BE=\frac{1632}{463}\Longrightarrow q=\boxed{463}$

~ Nafer

Solution 10

Making perpendicular lines from $D$ to $AC$ , meeting at $N$ ; from $E$ to $AB$ , meeting at $J$ . According to LOC, we can get that $\cos\angle{C}=\frac{3}{5}$ . So we get that $CN=\frac{18}{5};DN=\frac{24}{5};AN=AC-CN=\frac{52}{5}$ . Now we can see that $\tan\angle{DAN}=\frac{DN}{AN}=\frac{6}{13}$ . Now we see that in $\triangle{EJA}$ , assuming $EJ=6x;AJ=13x$ since $\tan\angle{JAE}=\tan\angle{DAN}$ . Now we need to find the tangent of $\angle{B}$ . Making a perpendicular line from $C$ to $AB$ at $M$ . We can see that $CM=\frac{168}{13};AM=\frac{70}{13};BM=AB-AM=13-\frac{70}{13}=\frac{99}{13}$ . We get that $\tan\angle{B}=\frac{56}{33}$ so $BJ=\frac{33}{56}*6x=\frac{99x}{28}$ . After getting AJ and BJ, we can get that $AB=AJ+BJ=\frac{463x}{28}=13$ , which means that $x=\frac{364}{463}$ . According to the similarity, $\frac{CM}{BC}=\frac{JE}{BE};BE=\frac{2535}{463}$ which $\boxed{463}$ is our answer ~bluesoul

Solution 11 (Ultimate Stewarts Bash)

First, apply Stewart's theorem to triangle $ABC$ with cevian $AD$ , from which we receive $AD=\frac{4\sqrt{41}}{\sqrt{5}}$ . Then, set $AE=y$ and $BE=x.$ Hence, $DE=9-x$ . Applying Stewart's on triangle $ACE$ , with cevian $AD$ , we receive that $y^2-x^2=169-\frac{66}{5}x$ . By also applying the sine ratio formula on triangles $ACD$ and $AEB$ , since these triangles share the same height, we get that $\frac{6}{x}=\frac{\frac{1}{2} \cdot 14 \cdot \frac{4\sqrt{41}}{\sqrt{5}}}{\frac{1}{2} \cdot 13 \cdot y}$ . Here, we can simplify to receive that $\frac{32144}{7605}x^2=y^2$ . We plug this into our earlier equation, and get that $\frac{24539}{7605}x^2=169-\frac{66}{5}x \implies 24539x^2+66 \cdot 39^2x-169 - 169 \cdot 39^2 \cdot 5=0.$ We then apply the quadratic formula (which may seem computationally intensive, but factoring kills it), and get $\frac{-66 \cdot 39^2 + \sqrt{66^2 \cdot 39^4+4(24539)(169 \cdot39^2 \cdot 5)}}{2 \cdot 24539}$ . (Note we only take the plus symbol instead of $\pm$ since $x > 0$ .) After factoring heavily, we get the answer to be $\frac{-33 \cdot 39^2+39 \cdot 13 \cdot 364}{24539} = \frac{2535}{463}$ , and the answer is $\boxed{463}.$

~SirAppel

@@ Line 40: / Line 40: @@
 Drop the altitude from A and call the base of the altitude Q. Also, drop the altitudes from E and D to AB and AC respectively. Call the feet of the altitudes R and S respectively.
-From here, we can use Heron's Formula to find the altitude. The area of the triangle is <math>\sqrt{21*6*7*8}</math> = 84. We can then use similar triangles with triangle AQC and triangle DSC to find DS=<math>\frac{24}{5}</math>. Consequently, from Pythagorean theorem, SC = <math>\frac{18}{5}</math> and AS = 14-SC = <math>\frac{52}{5}</math>. We can also use pythagorean triangle on triangle AQB to determine that BQ = <math>\frac{33}{5}</math>.
+From here, we can use Heron's Formula to find the altitude. The area of the triangle is <math>\sqrt{21*6*7*8} = 84</math>. We can then use similar triangles with triangle <math>AQC</math> and triangle <math>DSC</math> to find <math>DS=\frac{24}{5}</math>. Consequently, from Pythagorean theorem, <math>SC = \frac{18}{5}</math> and <math>AS = 14-SC = \frac{52}{5}</math>. We can also use the Pythagorean theorem on triangle <math>AQB</math> to determine that <math>BQ = \frac{33}{5}</math>.
-Label AR as y and RE as x. RB then equals 13-y. Then, we have two similar triangles.
+Label <math>AR</math> as <math>y</math> and <math>RE</math> as <math>x</math>. <math>RB</math> then equals <math>13-y</math>. Then, we have two similar triangles.
 Firstly: <math>\triangle ARE \sim \triangle ASD</math>. From there, we have <math>\frac{x}{y} = \frac{\frac{24}{5}}{\frac{53}{5}}</math>.
@@ Line 48: / Line 48: @@
 Next: <math>\triangle BRE \sim \triangle BQA</math>. From there, we have <math>\frac{x}{13-y} = \frac{\frac{56}{5}}{\frac{33}{5}}</math>.
-Solve the system to get <math>x = \frac{2184}{463}</math> and <math>y = \frac{4732}{463}</math>.  Notice that 463 is prime, so even though we use pythagorean theorem on x and 13-y, the denominator won't change. The answer we desire is <math>\boxed{463}</math>.
+Solve the system to get <math>x = \frac{2184}{463}</math> and <math>y = \frac{4732}{463}</math>.  Notice that 463 is prime, so even though we use the Pythagorean theorem on <math>x</math> and <math>13-y</math>, the denominator won't change. The answer we desire is <math>\boxed{463}</math>.
 ==Solution 3 (LoC and LoS bash)==
 Let <math>\angle CAD = \angle BAE = \theta</math>. Note by Law of Sines on <math>\triangle BEA</math> we have
-<cmath>\frac{BE}{\sin{\theta}} = \frac{AE}{\sin{B}} = \frac{AB}{\sin{BEA}}</cmath>
+<cmath>\frac{BE}{\sin{\theta}} = \frac{AE}{\sin{B}} = \frac{AB}{\sin{\angle BEA}}</cmath>
 As a result, our goal is to find <math>\sin{\angle BEA}</math> and <math>\sin{\theta}</math> (we already know <math>AB</math>).
 Let the foot of the altitude from <math>A</math> to <math>BC</math> be <math>H</math>. By law of cosines on <math>\triangle ABC</math> we have
 <cmath>169 = 196 + 225 - 2 \cdot 14 \cdot 15 \cdot \cos{C} \Rightarrow \cos{C} = \frac{3}{5}</cmath>
-It follows that <math>AH = \frac{56}{5}</math> and <math>HC = \frac{42}{5} \Rightarrow AD = \frac{12}{5}</math>.
+It follows that <math>AH = \frac{56}{5}</math> and <math>HC = \frac{42}{5} \Rightarrow HD = \frac{12}{5}</math>.
 Note that by PT on <math>\triangle AHD</math> we have that <math>AD^2 = \left(\frac{56}{5}\right)^2 + \left(\frac{12}{5}\right)^2 = \frac{656}{5}</math>. By Law of Sines on <math>\triangle ADC</math> (where we square everything to avoid taking the square root) we see
@@ Line 65: / Line 65: @@
 <math>\theta</math>, <math>\angle B</math>, and <math>\angle BEA</math> are all in the same triangle. We know they add up to <math>180^{\circ}</math>. There's a good chance we can exploit this using the identity <math>\sin{p} = \sin{180^{\circ}-p}</math>.
-We have that <math>\sin{180^{\circ} - (\theta + \angle B)} = \sin{\angle BEA} = \sin{\theta + \angle B}</math>. Success! We know <math>\sin{\theta}</math> and <math>\sin{\angle B}</math> already. Applying the <math>\sin</math> addition formula we see
+We have that <math>\sin{(180^{\circ} - (\theta + \angle B))} = \sin{\angle BEA} = \sin{(\theta + \angle B)}</math>. Success! We know <math>\sin{\theta}</math> and <math>\sin{\angle B}</math> already. Applying the <math>\sin</math> addition formula we see
 <cmath>\sin{\theta + \angle B} = \sin{\theta} \cos{\angle B} + \sin{\angle B} \cos{\theta} = \frac{6}{\sqrt{205}} \cdot \frac{33}{65} + \frac{56}{65} \cdot \frac{13}{\sqrt{205}}=\frac{1}{65 \cdot \sqrt{205}} (198 + 728) = \frac{926}{65 \sqrt{205}}.</cmath>
 This is the last stretch! Applying Law of Sines a final time on <math>\triangle BEA</math> we see
 <cmath>\frac{BE}{\sin{\theta}} = \frac{13}{\sin{BEA}} \Rightarrow \frac{BE}{\frac{6}{\sqrt{205}}} = \frac{13}{\frac{926}{65\sqrt{205}}} \Rightarrow \frac{BE}{6} = \frac{13 \cdot 65}{926} \Rightarrow \frac{13 \cdot 65 \cdot 6}{926} = BE = \frac{2535}{463}.</cmath>
 It follows that the answer is <math>\boxed{463}</math>.
+==Solution 4 (Ratio Lemma and Angle Bisector Theorem)==
+Let <math>AK</math> be the angle bisector of <math>\angle A</math> such that <math>K</math> is on <math>BC</math>.
+Then <math>\angle KAB = \angle KAC</math>, and thus <math>\angle KAE = \angle KAD</math>.
+By the Ratio Lemma,
+<math>\frac{BE}{KE} = \frac{BA}{KA} * \frac{\sin{BAE}}{\sin{KAE}}</math> and <math>\frac{CD}{KD} = \frac{CA}{KA} * \frac{\sin{CAD}}{\sin{KAD}}</math>.
+This implies that <math>\frac{BE}{KE*BA} = \frac{CD}{KD*CA}</math>.
+Thus, <math>\frac{BE}{KE} = \frac{13}{14} * \frac{6}{DK}</math>.
+<math>DK = CK - 6 = 14*15/27 - 6 = 16/9</math>. Thus, <math>\frac{BE}{KE} = \frac{13*54}{14*16}</math>.
+Additionally, <math>BE + KE = 13*15/27 = 65/9</math>. Solving gives that <math> q = 463.</math>
+Alternate:
+By the ratio lemma,
+<math>BD/DC = (13/14)*(\sin BAD/\sin DAC)</math>
+<math>EC/EB = (14/13)*(\sin EAC/\sin BAE)</math>
+Combining these, we get
+<math>(BD/DC)(14/13) = (EC/EB)(13/14)</math>
+<math>(3/2)(14/13)(14/13) = (15-x)(x)</math>
+<math>x = 2535/463</math>
+Thus, <math>q = 463</math>
+==Solution 5 (Isogonal lines with respect to A angle bisesector)==
+Since <math>AE</math> and <math>AD</math> are isogonal with respect to the <math>A</math> angle bisector, we have <cmath>\frac{BE}{EC}\cdot \frac{BD}{DC}=(\frac{AB}{AC})^2.</cmath>  To prove this, let <math>\angle BAE=\angle DAC=x</math> and <math>\angle BAD=\angle CAE=y.</math>  Then, by the Ratio Lemma, we have <cmath> \frac{BD}{DC}=\frac{AB\sin y}{AC\sin x}</cmath> <cmath> \frac{BE}{EC}=\frac{AB\sin x}{AC\sin y}</cmath> and multiplying these together proves the formula for isogonal lines. Hence, we have <cmath>\frac{BE}{15-BE}\cdot \frac{9}{6}=\frac{169}{196}\implies BE=\frac{2535}{463}</cmath> so our desired answer is <math>\boxed{463}.</math>
+==Solution 6 (Tangent subtraction formulas)==
+Note: We first recall some helpful tips regarding 13, 14, 15 triangles. Drawing an altitude H from B to AC results in AHB being a 5-12-13 right triangle and CHB being a 3-4-5 (9-12-15) right triangle.
+<center><asy>
+import olympiad; import cse5; import geometry; size(300);
+defaultpen(fontsize(10pt));
+defaultpen(0.8);
+dotfactor = 4;
+pair A = origin;
+pair C = rotate(15,A)*(A+dir(-50));
+pair B = rotate(15,A)*(A+dir(-130));
+pair D = extension(A,A+dir(-68),B,C);
+pair E = extension(A,A+dir(-82),B,C);
+label("$A$",A,N);
+label("$B$",B,SW);
+label("$D$",D,SE);
+label("$E$",E,S);
+label("$C$",C,SE);
+draw(A--B--C--cycle);
+draw(A--E);
+draw(A--D);
+draw(anglemark(B,A,E,5));
+draw(anglemark(D,A,C,5));
+pair G = foot(E,C,A);
+pair F = foot(D,C,A);
+draw(D--F);
+draw(E--G);
+label("$G$",G,N);
+label("$F$",F,N);
+</asy></center>
+Now we start by drawing altitudes from D and E onto AC, labeling them as F and G, and labelling <math>\angle DAG = \alpha</math>. Now we know that <math>\overline{DF} = \frac{24}{5}</math> and <math>\overline{FC} = \frac{18}{5}</math>. Therefore, <math>\overline{AF} = \frac{52}{5}</math>, so <math>\tan{(\alpha)} = \frac{6}{13}</math>. Our goal now is to use tangent <math>\angle EAG</math> in triangle <math>AEG</math>. We set <math>\overline{BE}</math> to <math>x</math>, so <math>\overline{ED} = 9 - x</math> and <math>\overline{EC} = 15 - x</math>, so <math>\overline{EG} = \frac{4}{5}(15-x)</math> and <math>\overline{GC} = \frac{3}{5}(15-x)</math> so <math>\overline{AG} = \frac{3x+25}{5}</math>. Now we just need tangent of <math>\angle EAG</math>.
+We find this using <math>\tan{(EAG)} = \tan{(A - \alpha)} = \frac{\tan{A} - \tan{\alpha}}{1 + \tan{A}\tan{\alpha}}</math>, which is <math>\frac{\frac{12}{5} - \frac{6}{13}}{1 + \frac{12}{5} \cdot \frac{6}{13}}</math> or <math>\frac{126}{137}</math>. Now we solve the equation <math>\tan{\angle EAG} = \frac{126}{137} = \frac{\frac{60-4x}{5}}{\frac{3x+25}{5}}</math>, so <math>x = \frac{2535}{463}</math>
+== Solution 8 (Isogonal Conjugates) ==
+Let <math>ED = x</math>, such that <math>BE = 9-x</math>. Since <math>\overline{AE}</math> and <math>\overline{AD}</math> are isogonal, we get <math>\frac{9-x}{6+x} \cdot \frac{9}{6} = \frac{13^2}{14^2} \Rightarrow 588(9 - x) = 338(6 + x)</math>, and we can solve to get <math>x = \frac{1632}{463}</math>(and <math>BE = \frac{2535}{463}</math>). Hence, our answer is <math>\boxed{463}</math>. - Spacesam
+== Solution 9 (Short and no IQ Required Altogether-Bash) ==
+Diagram borrowed from Solution 1.
+<center><asy>
+import olympiad; import cse5; import geometry; size(150);
+defaultpen(fontsize(10pt));
+defaultpen(0.8);
+dotfactor = 4;
+pair A = origin;
+pair C = rotate(15,A)*(A+dir(-50));
+pair B = rotate(15,A)*(A+dir(-130));
+pair D = extension(A,A+dir(-68),B,C);
+pair E = extension(A,A+dir(-82),B,C);
+label("$A$",A,N);
+label("$B$",B,SW);
+label("$D$",D,SE);
+label("$E$",E,S);
+label("$C$",C,SE);
+draw(A--B--C--cycle);
+draw(A--E);
+draw(A--D);
+draw(anglemark(B,A,E,5));
+draw(anglemark(D,A,C,5));
+</asy></center>
+Applying [[Law of Cosines]] on <math>\bigtriangleup ABC</math> with respect to <math>\angle C</math> we have
+<cmath>AB^2=AC^2+BC^2-2(AC)(BC)\cos C</cmath>
+Solving gets <math>\cos C=\frac{3}{5}</math>, which implies that
+<cmath>\sin C=\sqrt{1-\cos C}=\frac{4}{5}</cmath>
+Applying [[Stewart's Theorem]] with [[cevian]] <math>AD</math> we have
+<cmath>(BC)(AD)^2+(BC)(BD)(CD)=(CD)(AB)^2+(BD)(AC)^2</cmath>
+Solving gets <math>AD=\frac{4\sqrt{205}}{5}</math>.
+Applying [[Law of Sines]] on <math>\bigtriangleup ACD</math> to solve for <math>\sin CAD</math> we have
+<cmath>\frac{AD}{\sin C}=\frac{CD}{\sin CAD}</cmath>
+Solving gets <math>\sin CAD=\frac{6\sqrt{205}}{205}</math>. Thus <math>\sin BAE=\sin CAD=\frac{6\sqrt{205}}{205}</math>.
+Applying [[Law of Sines]] on <math>\bigtriangleup ABC</math> we have
+<cmath>\frac{AC}{\sin B}=\frac{AB}{\sin C}</cmath>
+Solving gets <math>\sin B=\frac{56}{65}</math>.
+Applying [[Stewart's Theorem]] with [[cevian]] <math>AE</math> we have
+<cmath>(BC)(AE)^2+(BC)(BE)(CE)=(CE)(AB)^2+(BE)(AC)^2</cmath>
+<cmath>(BC)(AE)^2+(BC)(BE)(BC-BE)=(BC-BE)(AB)^2+(BE)(AC)^2</cmath>
+Solving gets <math>AE=\sqrt{\frac{15BE^2-198BE+2535}{15}}</math>
+Finally, applying [[Law of Sines]] on <math>\bigtriangleup BAE</math> we have
+<cmath>\frac{AE}{\sin B}=\frac{BE}{\sin BAE}</cmath>
+<cmath>\frac{\sqrt{\frac{15BE^2-198BE+2535}{15}}}{\frac{56}{65}}=\frac{BE}{\frac{6\sqrt{205}}{205}}</cmath>
+<cmath>7605BE^2-32342BE+2535=0</cmath>
+Solving the easy quadratic equation gets <math>BE=\frac{1632}{463}\Longrightarrow q=\boxed{463}</math>
+~ Nafer
+== Solution 10 ==
+Making perpendicular lines from <math>D</math> to <math>AC</math>, meeting at <math>N</math>; from <math>E</math> to <math>AB</math>, meeting at <math>J</math>. According to LOC, we can get that <math>\cos\angle{C}=\frac{3}{5}</math>. So we get that <math>CN=\frac{18}{5};DN=\frac{24}{5};AN=AC-CN=\frac{52}{5}</math>. Now we can see that <math>\tan\angle{DAN}=\frac{DN}{AN}=\frac{6}{13}</math>. Now we see that in <math>\triangle{EJA}</math>, assuming <math>EJ=6x;AJ=13x</math> since <math>\tan\angle{JAE}=\tan\angle{DAN}</math>. Now we need to find the tangent of <math>\angle{B}</math>. Making a perpendicular line from <math>C</math> to <math>AB</math> at <math>M</math>. We can see that <math>CM=\frac{168}{13};AM=\frac{70}{13};BM=AB-AM=13-\frac{70}{13}=\frac{99}{13}</math>. We get that <math>\tan\angle{B}=\frac{56}{33}</math> so <math>BJ=\frac{33}{56}*6x=\frac{99x}{28}</math>.
+After getting AJ and BJ, we can get that <math>AB=AJ+BJ=\frac{463x}{28}=13</math>, which means that <math>x=\frac{364}{463}</math>. According to the similarity, <math>\frac{CM}{BC}=\frac{JE}{BE};BE=\frac{2535}{463}</math> which <math>\boxed{463}</math> is our answer
+~bluesoul
+== Solution 11 (Ultimate Stewarts Bash) ==
+First, apply Stewart's theorem to triangle <math>ABC</math> with cevian <math>AD</math>, from which we receive <math>AD=\frac{4\sqrt{41}}{\sqrt{5}}</math>. Then, set <math>AE=y</math> and <math>BE=x.</math> Hence, <math>DE=9-x</math>. Applying Stewart's on triangle <math>ACE</math>, with cevian <math>AD</math>, we receive that <math>y^2-x^2=169-\frac{66}{5}x</math>. By also applying the sine ratio formula on triangles <math>ACD</math> and <math>AEB</math>, since these triangles share the same height, we get that <math>\frac{6}{x}=\frac{\frac{1}{2} \cdot 14 \cdot \frac{4\sqrt{41}}{\sqrt{5}}}{\frac{1}{2} \cdot 13 \cdot y}</math>. Here, we can simplify to receive that <math>\frac{32144}{7605}x^2=y^2</math>. We plug this into our earlier equation, and get that <math>\frac{24539}{7605}x^2=169-\frac{66}{5}x \implies 24539x^2+66 \cdot 39^2x-169 - 169 \cdot 39^2 \cdot 5=0.</math> We then apply the quadratic formula (which may seem computationally intensive, but factoring kills it), and get <math>\frac{-66 \cdot 39^2 + \sqrt{66^2 \cdot 39^4+4(24539)(169 \cdot39^2 \cdot 5)}}{2 \cdot 24539}</math>. (Note we only take the plus symbol instead of <math>\pm</math> since <math>x > 0</math>.) After factoring heavily, we get the answer to be <math>\frac{-33 \cdot 39^2+39 \cdot 13 \cdot 364}{24539} = \frac{2535}{463}</math>, and the answer is <math>\boxed{463}.</math>
+~SirAppel
 == See also ==

2005 AIME II (Problems • Answer Key • Resources)
Preceded by Problem 13	Followed by Problem 15
1 • 2 • 3 • 4 • 5 • 6 • 7 • 8 • 9 • 10 • 11 • 12 • 13 • 14 • 15
All AIME Problems and Solutions

Page

Toolbox

Search