# How do you factor x²+8x+7?

Nov 7, 2015

$\left(x + 1\right) \left(x + 7\right)$

#### Explanation:

To quickly factor it, we want to find two numbers that add up to $8$ (the coefficient in front of x) and multiply to $7$ (the constant).

You might quickly see that the numbers we want are $1$ and $7$.

Next, simply write 2 pairs of parenthesis and put "$x +$" and the two magical numbers we just found...

$\left(x + 1\right) \left(x + 7\right)$

Notice if you were to FOIL this out, you would get the original expression. In fact, what we just did was FOIL-ing backwards.

Nov 7, 2015

${x}^{2} + 8 x + 7 = \left(x + 1\right) \left(x + 7\right)$

#### Explanation:

${x}^{2} + 8 x + 7$

Find two numbers that when added equal $8$ and when multiplied equal $7$. The numbers $1$ and $7$ meet the criteria.

${x}^{2} + 8 x + 7 = \left(x + 1\right) \left(x + 7\right)$