Basically the Remainder theorem states that the remainder of dividing a polynomial P(x) by (x - a) is given by P(a).
So for example if we divide x^ 2 - 2x + 7 by x - 2 the remainder will be
2^2 - 2(2) + 7 = 7..
If the remainder is 0 then the divisor will be a factor of the polynomial. This is the Factor Theorem and can be used to test if a given polynomial has a factor x-a.
