(a) In triangle ABC, angle A is greater than angle B. Prove that the length of side BC is greater than half the length of side AB. (b) In the convex quadrilateral ABCD, the angle at A is greater than the angle at C and the angle at D is greater than the angle at B. Prove that the length of side BC is greater than half of the length of side AD.(F Nazarov) geometrygeometric inequalityangles