In the given , the red areas are equal, and , where , and are coprime positive integers. Find .
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From the left figure, the red triangle is similar to △ A B C . Therefore, the ratio of their areas A △ A r e d = ( A D + D B ) 2 A D 2 = ( 5 + 1 ) 2 5 2 = 3 6 2 5 . ⟹ A r e d = 3 6 2 5 A △ , ⟹ A b l u e = A △ − A r e d = 3 6 1 1 A △ .
From the right figure,
A △ A b l u e ⟹ ( A E + E B ) 2 A E 2 A E + E B A E E B A E + 1 E B A E ⟹ E B A E = 3 6 1 1 = 3 6 1 1 = 6 1 1 = 6 1 1 = 6 − 1 1 1 1 = ( 6 − 1 1 ) ( 6 + 1 1 ) 1 1 ( 6 + 1 1 ) = 2 5 6 1 1 + 1 1 Taking square root both sides Divide up and down of LHS by E B
Therefore, a + b + c = 6 + 1 1 + 2 5 = 4 2 .