Answer:
the total area of the rhombus is 80 units².
Step-by-step explanation:
If we draw a horiz. line through the vertices (-1, 1) and (9, 1), we create a triangle with those points and (4, 9) as vertices. Thus, the base of this triangle is 9 - (-1), or 10, and the height is 9 - 1, or 8.
The area of this triangle is A = (1/2)(base)(height), or
A = (1/2)(10)(8) = 40 units². Since the lower triangle has the same area, the total area of the rhombus is 2(40 units²), or 80 units².
