2016 AIME I Problems/Problem 9
Triangle has and . This triangle is inscribed in rectangle with on and on . Find the maximum possible area of .
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, . Since . 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
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 .
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