You are told to divide a polynomial by a monomial, right? A monomial would be something like x + 3, and your polynomial could be something like x^2 + 7x + 12. The remainder theorem tells you that if you use long division to divide the polynomial by the monomial, if you have a remainder, the monomial is NOT a factor of the polynomial. You put the polynomial under the division sign and the monomial outside the division sign and do the dividing, just like you would if you had 80 under the division sign and 10 outside. When you divide the 80 by the 10, it comes out evenly with no remainder. Same thing with this: if you can divide x^2 + 7x + 12 by x + 3 and there is no remainder, then x + 3 is a factor of the polynomial. What's up on top above the division sign is the other factor. So when you multiply the x + 3 by what's on top, you get back your polyomial. It's really a very perfect and cool thing.