Factorise the tollowing expression `p^4` - `81 q^4 `

Explanation

`p^4-81q^4`

`=(p^2)^2-(9q^2)^2`

As `a^2-b^2 = (a+b)(a-b)`

So, our expression becomes,

`=(p^2+9q^2)(p^2-9q^2)`

`=(p^2+9q^2)(p^2-(3q)^2)`

`=(p^2+9q^2)(p+3q)(p-3q)`, which are the factors of the given expression.