Quadrilateral 



1. Classification of quadrilaterals
A quadrilateral is a polygon with four sides.
In the figure 2, we see that its opposite sides are parallel. The side AB is parallel to DC. DA and CB are also parallel. This quadrilateral is called a parallelogram.
The figure 3 has two parallel sides: AB with CD. But the other two sides are not parallel. It is called trapeze, which is a quadrilateral with two opposite sides parallel.
The Figure 1 does not have any parallel side and it is called trapezoid.
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