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Factoring or factorising in British English is the process of finding the factors an algebraic term, or writing a term as a multiple of more simple terms. It is the opposite of expanding. A simple example would be:
$3x + 9 = 3(x+3)$
With the first term being the expanded version and the second factored. A more complex example would be:
$2x^2 + 5x + 3 = (2x + 3)(x + 1)$

## Common factoring patterns

### Binomials

Binomials tend to appear by themselves as a square:

\begin{align} a^2+2ab+b^2 = (a+b)^2\\ a^2-2ab+b^2 = (a-b)^2\end{align}

If raised to higher powers, they continue according to the pattern shown in the Binomial coefficient:

$(a+b)^3 = a^3 + 3a^2b + 3 b^2a + b^3$

The Quadratic formula determines roots, which can be factored from the polynomial.

$f(x) = ax^2 + bx + c = 0,\quad a \ne 0$
$\displaystyle x = \frac{-b \pm \sqrt{b^2-4ac}}{2a}$

### Difference of squares

One common factoring problem is called a difference of squares. This involves a squared factor minus another squared factor. This type of equation can be written as follows:

$a^2 - b^2 = (a + b)(a - b)$

An example of this using real numbers would be:

$4x^2 - 9y^2 = (2x - 3y)(2x + 3y)$