A circle with radius 217 is inscribed in a right triangle with leg lengths a and b . The circumcircle of this triangle has radius 2017. What is a + b ?
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Why is r_i given by this formula?
Using Thales' Theorem we get that 2 0 1 7 = 2 x + y . Notice that r = 2 1 7 . From that
a + b = x + y + 2 r = 2 0 1 7 ∗ 2 + 2 1 7 ∗ 2 = 4 4 6 8
Why is the hypotenuse x+y?
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Lol just figured it out it's because of the tangent lines
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With the circumcircle's radius r c , we can see that the hypotenuse c of the triangle is 2 × r c = 4 0 3 4 .
Now, the radius r i of the incircle of a right triangle with sides a , b and hypotenuse c is given by r i = 2 a + b − c :
r i ⟹ a + b = 2 a + b − c = 2 r i + c = 2 ⋅ 2 1 7 + 4 0 3 4 = 4 4 6 8