How do I find the exact area of a triangle

Question

What's the exact area of triangle DEF shown in the graph?

	A)	24 square units
B)	18 square units
C)	36 square units
D)	15 square units

Answer 1

Put a point, Q, at (3, -3)

Area of ΔDQF = 24

Area of ΔDQE = 9

Area of ΔDEF = area of ΔDQF - area of ΔDQE

Answer 2

Build a rectangle around the triangle by letting A = (-3, 4) and B = (3,-4).

Then, Area of ΔDEF = Area of rectangle AFBD - Area of right ΔDBE - Area of right ΔDAF

= 48 - (1/2)(6)(2) - (1/2)(6)(8) = 48 - 6 - 24 = 18