Q.AOB is a diameter of the circle with center O, and C is a point on the circle. If \(\angle\)OBC = 60°, then find the measure of \(\angle\)OCA.

Because AOB is the diameter of the circle, \[ \therefore \angle ACB = 90^\circ \] So, \[ \angle BAC = 90^\circ - \angle ABC = 90^\circ - \angle OBC = 90^\circ - 60^\circ = 30^\circ \] \[ \therefore \angle OAC = 30^\circ \] Again, in triangle OCA, since OC = OA = radius of the circle, \[ \therefore \angle OCA = \angle OAC = 30^\circ \]
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