Find the area of parallelogram given A(2,1), B(7,1), C(9,5) and D(4,5).
1-I plotted each point on the xy-plane.
2-I determined the base to be 5 and the height to be 8.
3-I then used A = bh and found the area to be 40.
However, the math book tells me that the area is 20.
How can this be?