I finally did it
by djmathman, Sep 2, 2012, 12:36 AM
I remember in one of my posts back in November I wrote a passage that went something along the lines of
Look who bucked that prediction.
Solution
Quote:
Therefore, I will solve my first AIME #15 in
.

Look who bucked that prediction.
1997 AIME #15 wrote:
The sides of rectangle
have lengths
and
. An equilateral triangle is drawn so that no point of the triangle lies outside
. The maximum possible area of such a triangle can be written in the form
, where
,
, and
are positive integers, and
is not divisible by the square of any prime number. Find
.










Solution
Let
be a rectangle such that
and
. Place the rectangle on the complex plane, with
at the origin and
on the positive imaginary axis. It is clear that the maximum possible area of such a triangle will occur when the triangle is inscribed in the rectangle. Hence, place points
and
on
and
respectively such that
is equilateral. For some positive reals
and
, we can say that
and
. Since
is a
rotation of
clockwise about
, we can write the equation
![\[a+10i=e^{\pi i/3}(11+bi).\]](//latex.artofproblemsolving.com/0/5/a/05abc96389b5a140fd284cfd1a0bc8521625ffb9.png)
Expanding this gives us
Equating the imaginary parts of both sides gives us
, so
. This means that the square of the distance from
to the origin is
![\[\left|11+(20-11\sqrt{3})i\right|^2=11^2+(20-11\sqrt{3})^2=121+400-440\sqrt{3}+363=884-440\sqrt{3}.\]](//latex.artofproblemsolving.com/d/1/1/d11ae62554b2d371d2c6e4333be8e3e3744c7c41.png)
Finally, note that the area of the equilateral triangle is
. Since
is precisely what we calculated above, our final answer is
.


















![\[a+10i=e^{\pi i/3}(11+bi).\]](http://latex.artofproblemsolving.com/0/5/a/05abc96389b5a140fd284cfd1a0bc8521625ffb9.png)
Expanding this gives us

Equating the imaginary parts of both sides gives us



![\[\left|11+(20-11\sqrt{3})i\right|^2=11^2+(20-11\sqrt{3})^2=121+400-440\sqrt{3}+363=884-440\sqrt{3}.\]](http://latex.artofproblemsolving.com/d/1/1/d11ae62554b2d371d2c6e4333be8e3e3744c7c41.png)
Finally, note that the area of the equilateral triangle is



This post has been edited 1 time. Last edited by djmathman, Apr 6, 2015, 3:09 AM
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