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Problem 1087: Tangent Circles, Parallel, 15 Degrees, Angle
Level: High School, College, Math Education

The figure below shows the circles of centers O and Q tangent at A. BC is tangent to circle Q at C and parallel to OA. Prove that angle COB = 15 degrees.

Geometry Problem 1087 Tangent Circles, Parallel, 15 Degrees, Angle


Geometry problem solving is one of the most challenging skills for students to learn. When a problem requires auxiliary construction, the difficulty of the problem increases drastically, perhaps because deciding which construction to make is an ill-structured problem. By “construction,” we mean adding geometric figures (points, lines, planes) to a problem figure that wasn’t mentioned as "given."

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