Question: a parallelogram must be a rectangle when?
Answer: DEFINITION: A rectangle is a parallelogram with four right angles. THEOREM: If a parallelogram is a rectangle, it has congruent diagonals. THEOREM Converse: If a parallelogram has congruent diagonals, it is a rectangle. ... THEOREM: If a parallelogram is a rhombus, each diagonal bisects a pair of opposite angles.