By the side and base

The first way to calculate the area of a parallelogram is associated with one of the simplest shapes - a rectangle. Proof: if we draw a height h in a parallelogram, then we will divide it into two figures - a triangle and a trapezoid. Having made a simple movement of the triangle on the other side of the trapezoid, we get a rectangle equal in area to our parallelogram. And since the area of the rectangle is multiplied by its sides, in this case we will do the same, only instead of the length of the rectangle in the formula will be the side of the parallelogram, and instead of the width, its height as shown in the formula above.