# How do you simplify (x+3)(x-3)+(x+7)(x-3) ?

Aug 28, 2016

$2 {x}^{2} + 4 x - 30$

#### Explanation:

$\left(x + 3\right) \left(x - 3\right) + \left(x + 7\right) \left(x - 3\right)$

One method would be to multiply the brackets out and collect the like terms together.
This seems a long and tedious method - we will end up with 8 terms which need to be simplified.

We can also use a factoring method because there is a common bracket in each term.

$\left(x + 3\right) \textcolor{red}{\left(x - 3\right)} + \left(x + 7\right) \textcolor{red}{\left(x - 3\right)}$

$\textcolor{red}{\left(x - 3\right)} \left(x + 3 + x + 7\right)$

=$\textcolor{red}{\left(x - 3\right)} \left(2 x + 10\right)$

=$2 {x}^{2} + 10 x - 6 x - 30$

$2 {x}^{2} + 4 x - 30$