Question

Lines AB and AC tangent to circle k(O) at B and C respectively. Find BC, if m∠OAB=30°, and AB=5 cm.

Answer 1

5 cm

Explanation:

ΔABC is equilateral, so BC = AB = 5 cm.

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AO is the perpendicular bisector of BC and the angle bisector of angle A, so ∠OAC = ∠OAB = 30°. Then vertex angle BAC of isosceles triangle ABC is 60°, which means all angles in the triangle are 60° and the triangle is equilateral.