In a rectangular coordinate system, what is the area of a triangle whose vertices have the coordinates (2, 0), (7, 4), and (7, -4)?  Pick one.
A) 18	B) 19	C) 20	D) 21	E) 22
The triangle is symmetric about the x-axis.   The part above the x-axis forms a triangle with a base of 5 and a height of 4.   The area of this part is (1/2)(5)(4).   We can double this to find the area of the whole triangle.   The total area is (2)(1/2)(5)(4) = 20.   The answer is 20.
<result>C</result>
In a rectangular coordinate system, what is the area of a triangle whose vertices have the coordinates (2, 0), (7, 4), and (7, -4)?