2011 AIME II Problems/Problem 4
In triangle , . The angle bisector of $\ang A$ (Error compiling LaTeX. ! Undefined control sequence.) intersects at point , and point is the midpoint of . Let be the point of the intersection of and . The ratio of to can be expressed in the form , where and are relatively prime positive integers. Find .
Let be on such that . It follows that , so by the Angle Bisector Theorem. Similarly, we see by the midline theorem that . Thus, and .
Assign mass points as follows: by Angle-Bisector Theorem, , so we assign . Since , then , and .
By Menelaus' Theorem on with transversal ,
We will use barycentric coordinates. Let , , . By the Angle-Bisector Theorem, . Since is the midpoint of , . Therefore, the equation for line BM is . Let . Using the equation for , we get Therefore, so the answer is .
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