# How do you factor completely x^2 + 2x – 15?

Mar 2, 2018

See below...

#### Explanation:

To factorise, we firstly need two brackets, each containing an $x$.

$\left(x\right) \left(x\right)$

This creates the ${x}^{2}$ term.

Now we need to get the rest of the terms. To do this, we need two factors of $- 15$ which will add/subtract to give us $+ 2$

The two factors that do this are $- 3$ and $5$, as $- 3 + 5 = 2$

$\therefore \left(x - 3\right) \left(x + 5\right)$

You can check by expanding it out.

When looking for factors, if it is not obvious straight away then list them out and you'll eventually get there.