Rectangle
Definition
A plane convex quadrilateral is a rectangle if, and only if, all four angles are congruent. Note: Since all four angles are congruent and the sum of the internal angles of the quadrilateral is 360º, then each angle measures 90º.
Rectangle
Property of Rectangle
In every rectangle, all diagonals are congruent.
Argument
Exercise
Research and prove the argument of following property: Every parallelogram that has congruent diagonals is a rectangle."