2.11. State the converse of each of the following true statements. State whether the converse is necessarily true. (a) Half a right angle is an acute angle. (b) An obtuse triangle is a triangle having one obtuse angle. (c) If the umpire called a third strike, then the batter is out. (d) If I am taller than you, then you are shorter than 1. (e) If I am heavier than you, then our weights are unequal. 2.12. Prove each of the following. (a) Straight angles are congruent. (b) Complements of congruent angles are congruent. (c) Vertical angles are congruent.