Algebra
# Polynomial Arithmetic

Given that $x^2 - y^2 = (x-y) ( x+y)$, what is the value of $31 ^2 - 19 ^2$?

If $x+y=6$, $x-y=2$ and $x^2+y^2=20$, what is the value of $x^4-y^4?$

Evaluate the above expression.

Find the positive value of $N$ such that $N^2 = 169.$