In a rectangular coordinate system, what is the area of a triangle whose vertices have the coordinates (-1, 0), (7, 4), and (7, -4)?  Choose the correct choice from the following
A) 29  B) 30  C) 31  D) 32  E) 33
The triangle is symmetric about the x-axis.   The part above the x-axis forms a triangle with a base of 8 and a height of 4.   The area of this part is (1/2)(8)(4).   We can double this to find the area of the whole triangle.   The total area is (2)(1/2)(8)(4) = 32.   The answer is 32.
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In a rectangular coordinate system, what is the area of a triangle whose vertices have the coordinates (-1, 0), (7, 4), and (7, -4)?