# How do you factor y^2-49?

Jul 26, 2015

Rewrite the expression as a difference of two perfect squares.

#### Explanation:

You can factor the difference of two perfect squares by using the formula

${a}^{2} - {b}^{2} = \left(a - b\right) \left(a + b\right)$

You already have one perfect square, ${y}^{2}$, now all you have to do is write $49$ as a perfect square, too.

$49 = 7 \cdot 7 = {7}^{2}$

The original expression now becomes

${y}^{2} - {7}^{2} = \textcolor{g r e e n}{\left(y + 7\right) \left(y - 7\right)}$