# Polynomials

Polynomials: a mathematical expressions consisting of variables and coefficients, combined using addition, subtraction, and multiplication operations. The order or degree of the polynomial is determined by the highest power of the variable within the expression. Polynomials form the backbone of various mathematics fields like algebra and calculus, allowing for diverse applications. They aid in modeling various phenomena in physics, economics, machine learning algorithms, and in developing strategies in game theory.

Polynomials are linear combinations of powers of x. The highest power is the order of the polynomial. For example, a cubic is a polynomial of order 3. (What does the word ‘polynomial’ mean?).

You may be required to manipulate polynomials including expanding brackets, simplifying expressions and factorising. There may also be questions involving Polynomial Division and/or with the use of Factor Theorem.

## Manipulating Polynomials

1. Expanding and Simplifying– To expand and simpify – this works in the same way as expanding double brackets but you should end up with 6 terms before simplification:
2. Factorising Cubics– they may ask you to factorise , for example. The trick is to inspect the cubic and see if you can guess a root. In this case, is a root since it gives . It follows that is a factor.  We show that by guessing the quadratic inside the brackets and expanding then improving.  See the Cubics page, Example 2.2 for another example. Alternatively, you can use polynomial division as below. Fully factorised .

## Factor Theorem & Polynomial Division

1. Factor Theorem– Factor theorem states that if a polynomial is divisible by then and vice versa. It follows from this that if a polynomial is divisible by then and vice versa. For example, if is a factor of , then . Similarly, if then is a factor. In simpler cases, if , for example, then is a factor of . Simplify a problem by identifying a factor of a polynomial before you use polynomial division (see below).
2. Polynomial Division– Polynomial Division combines algebra with the technique of long division. The idea is to identify the factor required for the left most term in each step. This factor then goes on top. For example, in the Extra Resources below, a cubic polynomial with a term is being divided by a linear function with an term. The missing factor is thus . This is then multiplied by to see what remains to find.

## Examples

1. Expand and simplify .
2. Factorise fully .

Solution:

1. Start by multiplying out one pair of brackets: . Then multiply out the rest: .
2. By inspection, we can see that is a factor of . This can be seen by evaluating and using Factor Theorem above. It then remains to see what the quadratic factor will be. Again, by inspection (guessing and multiplying out rather than using polynomial division) we have Finally, we factorise the quadratic to give .

1. Show that is divisible by .
2. Given that , factorise fully .

Solution:

1. The easiest way to do this is to use factor theorem. Factor theorem states that is divisible by if .
Hence is a factor of and is divisible by .
2. According to Factor Theorem, if then is a factor and we can write . We identify the quadratic factor  by inspection â€“ in order to get as the first term when expanding, the first term in the quadratic must be . Since the expansion gives the correct term we donâ€™t require an term in the quadratic. It remains to find the constant term which can be seen from the final term in . We factorise the quadratic term itself as since once a 2 is factored out, a difference of squares remains. We have .

## Videos

Factor Theorem and Remainder Theorem all rolled in with Simultaneous Equations and factorising a cubic.