## Geometry: Common Core (15th Edition)

We have two adjacent sides congruent; this means opposite sides are congruent, so all sides are congruent. One angle is a right angle, so we can say that all angles are right angles because any angle opposite to this angle is congruent and will be a right angle. Consecutive angles are supplementary, so any consecutive angles to this angle will also have measures of $90^{\circ}$. A parallelogram with all sides congruent and all angles congruent is a square.