ELI5: Explain Like I'm 5

Polynomial remainder theorem

Okay, so imagine you have a cake and you want to share it equally among your friends. You cut the cake into equal slices, but there might still be some leftover cake. You can call this leftover cake the "remainder".

Now, let's say you have a math problem that involves a thing called a polynomial, which is basically just a bunch of numbers and variables all mashed together. Sometimes you might need to divide one polynomial by another polynomial, like how you divide the cake slices among your friends. And just like with the cake, there might be some leftover "remainder" after you do the division.

The polynomial remainder theorem is a rule that tells you how to figure out what the remainder is when you divide a polynomial by another polynomial. It's like a recipe that helps you solve this math problem.

Here's how it works: let's say you have two polynomials, let's call them "P" and "Q". If you divide P by Q, and the remainder is "R", then the polynomial remainder theorem tells you that you can find R by plugging in a certain number into the polynomial Q. That number is the same as the degree (or the highest power) of the polynomial P.

Okay, that might sound confusing, so let's break it down further. When we say "degree of a polynomial", we mean the highest power of the variable in that polynomial. For example, if you have the polynomial "3x^2 + 4x + 1", then the degree of that polynomial is 2, because that's the highest power of "x" (which is 2).

Now, let's go back to our cake analogy. If you have a cake and you're cutting it into slices, the size of the slices depends on how many friends you have. If you have more friends, then each slice will be smaller, and there will be more leftover cake. If you have fewer friends, then each slice will be bigger, and there will be less leftover cake.

Similarly, the size of the "remainder" in the polynomial division depends on the degree of the polynomial you're dividing by. If the degree of Q is high (meaning it has a lot of variables or a high power), then it's harder to divide P by Q and there might be a bigger remainder. If the degree of Q is low, then it's easier to divide P by Q and there might be a smaller remainder.

So, to figure out the remainder using the polynomial remainder theorem, you first need to know the degree of P. Once you know that, you can plug that number into Q (with a negative sign in front), and then solve for the remainder R.

Here's an example: let's say you have the polynomials "P = x^3 + 2x^2 + 3x + 4" and "Q = x - 1". To use the polynomial remainder theorem, we need to find the degree of P, which is 3 (because that's the highest power of x in P). Then, we plug in "-3" (since we need to use the negative degree of P) into Q, like this:

Q(-3) = (-3) - 1 = -4

So the remainder R is -4. This means that if we divide P by Q, we'll get a quotient (the part of the answer that's "evenly" divisible by Q) and a remainder of -4.

And that's basically the polynomial remainder theorem! It's a way to find the leftover "cake" when you divide one polynomial by another.