A parallelogram is a quadrilateral (four-sided figure) whose opposite sides are parallel, and whose opposite angles, therefore, are equal. The diagonals of a parallelogram bisect each other. A parallelogram of base b and height h has an area:
A = bh = ab sinA = ab sinB.
The height of a parallelogram is h = a sinA = a sinB. The sides a, b, c, and d and diagonals p and q of a parallelogram satisfy the equality:
p2 + q2 = a2 + b2 + c2 + d2
Special cases of a parallelogram are a rhombus, which has sides of equal length, a rectangle, which has two sets of parallel sides that are perpendicular to each other, and a square, which meets the conditions of both a rectangle and a rhombus.