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Printimc
geometry intermediate
Problem
Circles with centers and have radii and , respectively, and are externally tangent. Points and on the circle with center and points and on the circle with center are such that and are common external tangents to the circles. What is the area of the concave hexagon ? 
(A)
(B)
(C)
(D)
Solution
When we see this problem, it practically screams similar triangles at us. Extend to the left until it intersects lines and at point . Triangles and are similar, and by symmetry, so are triangles and . Then, the area of kite is just and the area of kite is (using our similarity ratios). The difference of these yields the area of hexagon or .
Final answer
B