Copy of Parallelogram = Parallelogram
Corollary 1:
The area of a parallelogram is equal to area of a rectangle on the same base and between same parallels. In fact, a rectangle is also a parallelogram. We may replace the parallelogram by rectangle and proceed in the same way to prove the corollary.
Corollary 2:
Area of a parallelogram = base x height
In the figure DA is the altitude of both the rectangle ABCD and the parallelogram ABEF.
Now, area of parallelogram ABEF = Area of rectangle ABCD
= AB x DA
Area of parallelogram = base x height.
Corollary 3:
Parallelograms on the equal base and between the same parallels are equal in area.