Difference between revisions of "1998 AIME Problems/Problem 6"

(prob / sol)
m (Solution: downsize slightly)
Line 3: Line 3:
  
 
== Solution ==
 
== Solution ==
[[Image:AIME_1998-6.png|500px]]
+
[[Image:AIME_1998-6.png|350px]]
  
 
There are several [[similar triangles]]. <math>\triangle PAQ \displaystyle \sim \triangle PDC</math>, so we can write the [[proportion]]:
 
There are several [[similar triangles]]. <math>\triangle PAQ \displaystyle \sim \triangle PDC</math>, so we can write the [[proportion]]:
Line 28: Line 28:
 
</div>
 
</div>
  
Thus, <math> RC = \sqrt{112*847} = 308 \displaystyle</math>.  
+
Thus, <math> RC = \sqrt{112*847} = 308 \displaystyle</math>.
  
 
== See also ==
 
== See also ==

Revision as of 21:03, 7 September 2007

Problem

Let $A\displaystyle BCD$ be a parallelogram. Extend $\overline{DA}$ through $A$ to a point $P,$ and let $\overline{PC}$ meet $\overline{AB}$ at $Q$ and $\overline{DB}$ at $R.$ Given that $PQ = 735$ and $QR = 112,$ find $RC.$

Solution

AIME 1998-6.png

There are several similar triangles. $\triangle PAQ \displaystyle \sim \triangle PDC$, so we can write the proportion:

$\frac{AQ}{CD} = \frac{PQ}{PC} = \frac{735}{112 + 735 + RC} = \frac{735}{847 + RC}$

Also, $\triangle BRQ \displaystyle \sim DRC$, so:

$\displaystyle \frac{QR}{RC} = \frac{QB}{CD} = \frac{112}{RC} = \frac{CD - AQ}{CD} = 1 - \frac{AQ}{CD} \displaystyle$

$\frac{AQ}{CD} = 1 - \frac{112}{RC} = \frac{RC - 112}{RC}$

Substituting,

$\frac{AQ}{CD} = \frac{735}{847 + RC} = \frac{RC - 112}{RC}$

$\displaystyle735RC = (RC + 847)(RC - 112)$
$0 = RC^2 - 112\cdot847$

Thus, $RC = \sqrt{112*847} = 308 \displaystyle$.

See also

1998 AIME (ProblemsAnswer KeyResources)
Preceded by
Problem 5
Followed by
Problem 7
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
All AIME Problems and Solutions