In the diagram below, angle is a right angle. Point is on , and bisects angle . Points and are on and , respectively, so that and . Given that and , find the integer closest to the area of quadrilateral .
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By the Pythagorean Theorem, B C = 3 5 . Letting B D = x we can use the angle bisector theorem on triangle A B C to get x / 1 2 = ( 3 5 − x ) / 3 7 , and solving gives B D = 6 0 / 7 and D C = 1 8 5 / 7 .
The area of triangle A G F is 1 0 / 3 that of triangle A E G , since they share a common side and angle, so the area of triangle A G F is 1 0 / 1 3 the area of triangle A E F .
Since the area of a triangle is 2 a b sin C , the area of A E F is 5 2 5 / 3 7 and the area of A G F is 5 2 5 0 / 4 8 1 .
The area of triangle A B D is 3 6 0 / 7 , and the area of the entire triangle A B C is 2 1 0 . Subtracting the areas of A B D and A G F from 2 1 0 and finding the closest integer gives 1 4 8 as the answer.