Difference between revisions of "2016 AIME I Problems/Problem 9"
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− | Note that if angle <math>BAC</math> is obtuse, it would be impossible for the triangle to inscribed in a rectangle. This can easily be shown by drawing triangle ABC, where <math>A</math> is obtuse. Therefore, angle A is acute. Let angle <math>CAS=n</math> and angle <math>BAQ=m</math>. Then, <math>\overline{AS}=31\cos(n)</math> and <math>\overline{AQ}=40\cos(m)</math>. Then the area of rectangle <math>AQRS</math> is <math>1240\cos(m)\cos(n)</math>. By product-to-sum, <math>\cos(m)\cos(n)=\frac{1}{2}(\cos(m+n)+\cos(m-n))</math>. | + | Note that if angle <math>BAC</math> is obtuse, it would be impossible for the triangle to inscribed in a rectangle. This can easily be shown by drawing triangle ABC, where <math>A</math> is obtuse. Therefore, angle A is acute. Let angle <math>CAS=n</math> and angle <math>BAQ=m</math>. Then, <math>\overline{AS}=31\cos(n)</math> and <math>\overline{AQ}=40\cos(m)</math>. Then the area of rectangle <math>AQRS</math> is <math>1240\cos(m)\cos(n)</math>. By product-to-sum, <math>\cos(m)\cos(n)=\frac{1}{2}(\cos(m+n)+\cos(m-n))</math>. <math>\cos(m+n)=\sin(90-m-n)=\sin(BAC)=\frac{1}{5}</math>. The maximum possible value of <math>\cos(m-n)</math> is 1, which occurs when <math>m=n</math>. Thus the maximum possible value of <math>\cos(m)\cos(n)</math> is <math>\frac{1}{2}(\frac{1}{5}+1)=\frac{3}{5}</math> so the maximum possible area of <math>AQRS</math> is <math>1240\times{\frac{3}{5}}=\fbox{744}</math>. |
-AkashD | -AkashD | ||
Revision as of 22:29, 7 March 2016
Contents
Problem
Triangle has
and
. This triangle is inscribed in rectangle
with
on
and
on
. Find the maximum possible area of
.
Solution
Solution 1
Note that if angle is obtuse, it would be impossible for the triangle to inscribed in a rectangle. This can easily be shown by drawing triangle ABC, where
is obtuse. Therefore, angle A is acute. Let angle
and angle
. Then,
and
. Then the area of rectangle
is
. By product-to-sum,
.
. The maximum possible value of
is 1, which occurs when
. Thus the maximum possible value of
is
so the maximum possible area of
is
.
-AkashD
Solution 2
As above, we note that angle must be acute. Therefore, let
be the origin, and suppose that
is on the positive
axis and
is on the positive
axis. We approach this using complex numbers. Let
, and let
be a complex number with
,
and
. Then we represent
by
and
by
. The coordinates of
and
depend on the real part of
and the imaginary part of
. Thus
We can expand this, using the fact that
, finding
Now as
, we know that
. Also,
, so the maximum possible imaginary part of
is
. This is clearly achievable under our conditions on
. Therefore, the maximum possible area of
is
.
Solution 3 (With Calculus)
Let be the angle
. The height of the rectangle then can be expressed as
, and the length of the rectangle can be expressed as
. The area of the rectangle can then be written as a function of
,
. For now, we will ignore the
and focus on the function
.
Taking the derivative, . Setting this equal to
, we get
. Since we know that
, the
solution is extraneous. Thus, we get that
.
Plugging this value into the original area equation, . Using a product-to-sum formula, we get that:
.
Note
It has been noted that this answer won't actually work. Let angle and angle
as in Solution 1. Since we know (through that solution) that
, we can call them each
. The height of the rectangle is
, and the distance
. We know that, if the triangle is to be inscribed in a rectangle,
.
However, , so the triangle does not actually fit in the rectangle: specifically, B is above R and thus in the line containing segment QR but not on the actual segment or in the rectangle.
See Also
2016 AIME I (Problems • Answer Key • Resources) | ||
Preceded by Problem 8 |
Followed by Problem 10 | |
1 • 2 • 3 • 4 • 5 • 6 • 7 • 8 • 9 • 10 • 11 • 12 • 13 • 14 • 15 | ||
All AIME Problems and Solutions |
The problems on this page are copyrighted by the Mathematical Association of America's American Mathematics Competitions.