1.a) Prove: if every angle of a polygon is acute, then the polygon is a triangle. That is, it can't be a quadrilateral, or a pentagon, or any n-gon with n > 3.
b) If a polygon has one right angle and otherwise acute angles, how many sides can it have? Prove your answer.
c) If a polygon has at most one non-acute angle, how many sides can it have? In your proofs, you may use standard facts about angles in polygons.