## Elementary Geometry for College Students (7th Edition)

(a) A quadrilateral with four congruent sides is a rhombus. (b) A quadrilateral that is a parallelogram with a right angle is a rectangle. Note that if one angle of a parallelogram is a right angle, then the opposite angle is a right angle. Then all four angles must be right angles since the sum of the angles is $360^{\circ}$