can you prove without using cross product?
(a+c,b+d)
(a+c,b+d)
(c,d)
c,
(c,d)
(a,b)
0,0
(0,0)
0,0)
Figure 3: Idea for a proof of the formula for the area of a parallelogram with vertices at (0,0), (a, b) (a + c, b + d), and (c, d), where a, b, c, d > 0. The first and third parallelograms have the same area. The lower left vertex is at (0,0) in all the figures. What are the coordinates of all the vertices in the second and third picture? What is the base and the height of the third parallelogram?