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geometry intermediate
Problem
In triangle , angle is 50 degrees, and angle is 70 degrees. Let be the foot of the perpendicular from to , the center of the circle circumscribed about triangle , and the other end of the diameter which goes through . Find the angle , in degrees.

Solution
Since triangle is right, .
Also, . Since triangle is isosceles with , . Hence, .
Also, . Since triangle is isosceles with , . Hence, .
Final answer
20^\circ