### Home > PC3 > Chapter 13 > Lesson 13.1.2 > Problem13-28

13-28.

Factor each of the following expressions.

Remember that a difference of two squares has a special factoring pattern.

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

1. $x^{2} − 4$

1. $9y^{2} − 81$

Factor out a $9$ first.

1. $1 − x^{2}$

1. $1−\sin^2\left(x\right)$

Think of $\sin^2\left(x\right)$ as one big variable (like $w^{2}$).