Quadrilateral ABCD above is shown to have three right angles. The fourth
angle therefore also measures 90 degrees, and ABCD is a rectangle. The
perimeter of a rectangle is equal to the sum of the lengths of the four sides,
which is equivalent to 2(length + width).
Area of Rectangle = length × widthThe area of a 7-by-3 rectangle is 7 × 3 = 21.
90 . Characteristics of a Parallelogram
A parallelogram has two pairs of parallel sides. Opposite sides are equal.
Opposite angles are equal. Consecutive angles add up to 180 degrees.
In the figure above, s is the length of the side opposite the 3, so s = 3.