Quadrilateral whose opposite sides are congruent and whose opposite angles are congruent.
- A parallelogram is a quadrilateral whose opposite sides are parallel in pairs.
- A parallelogram usually does not have an axis of symmetry.
However, except if it is a rectangle (having right angles), or isosceles (having adjacent congruent sides), the parallelogram has two perpendicular axes of symmetry. In this case, the parallelogram belongs to the class of rectangles, rhombuses, or both (square).
- Based on its properties, the parallelogram also belongs to the family of convex quadrilaterals and trapezoids.
Consider the parallelogram below :
- The formula to calculate the perimeter P of a parallelogram of side lengths a and b is: \(P=2 \times \left ( a+b \right )\).
- The formula to calculate the area A of a parallelogram with a base b and a height h is: \(A=b \times h\).
In the figure above, the opposite sides (hash marks) are congruent and the opposite angles (arcs) are congruent.