In a rectangular coordinate system, what is the area of a triangle whose vertices have the coordinates (-3, 0), (7, 4), and (7, -4)? Choose the correct choice from the following answers
A) 20
B) 25
C) 30
D) 35
E) 40
The triangle is symmetric about the x-axis.   The part above the x-axis forms a triangle with a base of 10 and a height of 4.   The area of this part is (1/2)(10)(4).   We can double this to find the area of the whole triangle.   The total area is (2)(1/2)(10)(4) = 40.   The answer is 40.
<result>E</result>
In a rectangular coordinate system, what is the area of a triangle whose vertices have the coordinates (-3, 0), (7, 4), and (7, -4)?