Let's define . So when we divide it by 'x+1', we can use Bezout's Theorem which states: that any polynomial(P(X)) divided by another binomial in the form 'x - a', then the remainder will be P(a).
We can use this fact to determine the remainder, because we divided our P(X) by x + 1 which is the same as x - (-1). So we plug in P(-1).
