Definition: A rectangle is a quadrilateral whose :
1. All angles are of 90 Degree (right angled at each vertex)
2. Opposite sides are equal and parallel to each other
In the following figure
Angles A, B, C and D = 90 degree
Line AB = CD
Line AC = BD
Line AB // CD
Line AC // BD
Hence, we can say that quadrilateral ABCD is a rectangle.

