Rectangle A rectangle has two pairs of equal sides. It has four right angles (90°). The opposite sides are parallel. The diagonals bisect each other. The exterior angles of a rectangle are each 90°.

The rectangle is a wobbly, unstable shape. When you push the side, it flops into a slanted parallelogram. This happens without any of the rectangle's sides changing length. Push Braced Rectangle ...

Identify the parallel sides 𝒂 and 𝒃, and the perpendicular height (𝒉). The parallel sides are 13 cm and 21 cm. The height is at right angles to the parallel sides. The height is 10 cm.