In a rectangular coordinate system, what is the area of a triangle whose vertices have the coordinates (3, 0), (6, 3), and (6, -3)?  Options
A) 9 B) 10 C) 11 D) 12 E) 13

Rationale: the triangle is symmetric about the x - axis . the part above the x - axis forms a triangle with a base of 3 and a height of 3 . the area of this part is ( 1 / 2 ) ( 3 ) ( 3 ) . we can double this to find the area of the whole triangle . the total area is ( 2 ) ( 1 / 2 ) ( 3 ) ( 3 ) = 9 . the answer is a .
Answer: A