Question

Find the product of $(x+y+z)$ and $(x+y-z)$.

Answer 1

We need to find the product of $(x+y+z)$ and $(x+y-z)$

Their product is:

$=x(x+y-z)+y(x+y-z)+z(x+y-z)$

$=x^2+xy-xz+xy+y^2-yz+zx+yz-z^2$

$=x^2+y^2-z^2+2xy$