Question

How do you factor `81x^2-1`?

Answer 1

`=color(blue)((9x+1)(9x-1)`

Explanation:

-As per the identity:

`color(blue)((a^2-b^2) = (a+b)(a-b)`

Here :
`color(blue)(9x) = a`
`color(blue)(1) =b`

Applying the identity to the expression:
`81x^2 - 1 =color(blue)( (9x)^2 -1^2`

`=color(blue)((9x+1)(9x-1)`