# How do you factorise 5n - 2a n - 5m + 2a m?

May 21, 2017

$= \left(n - m\right) \left(5 - 2 a\right)$

#### Explanation:

There are 4 terms - group the terms in pairs, making sure there is a $+$ sign between the pairs:

$\left(5 n - 5 m\right) + \left(- 2 a n + 2 a m\right) \text{ } \leftarrow$ take out common factors:

$= 5 \left(n - m\right) \textcolor{m a \ge n t a}{- 2} a \left(n - m\right) \text{ } \leftarrow$ note the change of signs.

$= \left(n - m\right) \left(5 - 2 a\right)$