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Printjmc
geometry junior
Problem
The sides of triangle are tangent to a circle with center as shown. Given that and , find , in degrees.

Solution
The circle with center is the incircle of . So, any segment from a vertex of the triangle to is an angle bisector.
From , we find that because is an angle bisector.
The sum of the measures of the internal angles of a triangle is , so
This yields .
From , we find that because is an angle bisector.
The sum of the measures of the internal angles of a triangle is , so
This yields .
Final answer
55^\circ