In triangle ABC the medians AD and CE have lengths 18 and 27, respectively, and AB=24. Extend CE to intersect the circumcircle of ABC at F. The area of triangle AFB is mn, where m and n are positive integers and n is not divisible by the square of any prime. Find m+n.
A number or a short expression. Fractions can be typed as 3/2, and spacing doesn't matter.
Solution
Applying Stewart's Theorem to medians AD,CE, we have:
BC2+4⋅182242+4⋅272=2(242+AC2)=2(AC2+BC2)
Substituting the first equation into the second and simplification yields 242=2(3AC2+2⋅242−4⋅182)−4⋅272⟹AC=25⋅3+2⋅35+24⋅33−27⋅3=370. By the Power of a Point Theorem on E, we get EF=27122=316. The Law of Cosines on △ACE gives
cos∠AEC=(2⋅12⋅27122+272−9⋅70)=83
Hence sin∠AEC=1−cos2∠AEC=855. Because △AEF,BEF have the same height and equal bases, they have the same area, and [ABF]=2[AEF]=2⋅21⋅AE⋅EFsin∠AEF=12⋅316⋅855=855, and the answer is 8+55=063.
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