### Теория:

Introduction:
A parallelogram is a special kind of quadrilateral in which both pairs of opposite sides are parallel.
In the following figure, you can see that $\mathit{AB}\parallel \mathit{CD}$ and $\mathit{BC}\parallel \mathit{AD}$

The four basic properties of a parallelogram are:
1. Opposite sides of a parallelogram are equal
2. Opposite angles of a parallelogram are equal
3. Diagonals divide the parallelogram into two congruent triangles
4. Diagonals bisect each other
There are three special types of a parallelogram, they are:
1. Rectangle
2. Rhombus
3. Square
The following figure explains the special types of a parallelogram.

Important things to know about parallelogram
Area of a parallelogram
The area is the base times the height.
area$$= b × h$$
($$h$$ is at right angles to $$b$$)
The Perimeter of a parallelogram
The perimeter is the distance around the edges.
The perimeter is $$2$$ times the (base + side length):
Perimeter$$= 2(b+l)$$
Diagonals of a parallelogram
The diagonals of a parallelogram bisect each other.
In other words, the diagonals intersect each other at the half-way point.
In the next chapter, we will explore the properties of a parallelogram.

Interesting fact:
A parallelogram where all angles are right angles is a rectangle!