O is the center of the circle, and the measure of ∠O is 70°.What is the measure of ∠OAB?

55°

Explanation

Let x = m∠OAB. OA = OB since radii of the same circle have equal measures. Therefore, m∠OAB = m∠OBA. x + x + 70 = 180 2x + 70 = 180 2x = 180 − 70 = 110 x = 110 ÷ 2 = 55