Question
[Geometry -- Triangle / Incircle, Very Hard, TITA]
In triangle , , and . Let be the midpoint of side , and let be the point at which the incircle of triangle touches side . The value of is ____.
Answer
Detailed solution
[Incircle touch point to midpoint of opposite side]
With , , , semi-perimeter . Tangent length from : .
Median length. By Apollonius for median from to mid-:
$
AM^{2} = \frac{2b^{2} + 2c^{2} - a^{2}}{4} = \frac{2(225) + 2(196) - 169}{4} = \frac{673}{4}.
$
Angle . Apply the law of cosines in , with :
$
BM^{2} = AB^{2} + AM^{2} - 2 AB\cdot AM\cos\angle BAM \Rightarrow \tfrac{169}{4} = 196 + \tfrac{673}{4} - 14\sqrt{673}\cos\angle BAM,
$
$
\Rightarrow 14\sqrt{673}\cos\angle BAM = 322 \Rightarrow \cos\angle BAM = \tfrac{23}{\sqrt{673}}.
$
Apply law of cosines in : , :
$
MP^{2} = 64 + \tfrac{673}{4} - 2 \cdot 8 \cdot \tfrac{\sqrt{673}}{2} \cdot \tfrac{23}{\sqrt{673}} = 64 + \tfrac{673}{4} - 184 = \tfrac{193}{4}.
$
So . Answer: 193.
Why CAT-level: Coordinate geometry works but produces fractions with denominator . The slick path requires combining median formula + law of cosines, an approach not directly signalled by the problem.