## Elementary and Intermediate Algebra: Concepts & Applications (6th Edition)

$$A=\frac{x^2+xy}{2}-y^2$$
We use the equation for the area of a triangle to find: $$A=\frac{1}{2}bh \\ A=\frac{1}{2}\left(x-y\right)\left(x+2y\right) \\ A=\frac{x^2+xy}{2}-y^2$$