The area derivation formula of parallelogram is: from the vertex of an obtuse angle of parallelogram perpendicular to the opposite side, the triangle cut by parallelogram is translated to the opposite side and added to form a rectangle. Compared with the original parallelogram, the circumference of the rectangle has changed and the area remains the same. At this time, the length of rectangle is the base of parallelogram, and the width of rectangle is the height of parallelogram. Because the area of a rectangle is equal to the length times the width, and the area of a parallelogram is equal to the bottom times.