Browse · harp
Printsmc
geometry senior
Problem
In the diagram, if points and are points of tangency, then equals: 
(A)
(B)
(C)
(D)
(E)
Solution
First we extend the line with and the line with so that they both meet the line with , forming an equilateral triangle. Let the vertices of this triangle be , , and . We know it is equilateral because of the angle of shown, and because the tangent lines and are congruent. We can see, because , , and are points of tangency, that circle is inscribed in . The height of an equilateral triangle is exactly times the radius of a circle inscribed in it. Let the height of be . We can see that the radius of the circle equals . Thus Subtracting from gives us so our answer is .
Final answer
E