# How do you factor #49x ^ { 2} - 81#?

##### 2 Answers

Aug 6, 2017

#### Explanation:

To make this more like a quadratic equation, we can add (without changing the value)

Factorise.

Hence:

Notice that

Aug 6, 2017

#### Explanation:

This is an identity known as the difference of two squares:

The clues to look for are:

#2# terms with a minus sign- perfect squares
- even indices