# How do you factor y=x^2 - 4x - 21 ?

Jul 27, 2016

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

#### Explanation:

Find factors of 21 which subtract to make 4.

Signs will be different, with more negatives.,

$7 \times 3 = 21 \text{ } 7 - 3 = 4$

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