Factorise. (i) `a^4 - b^4` (ii) `p^4 - 81` (iii) `x^4-(y+z)^4` (iv) `x^4-(x-z)^4`
(v) `a^2-2a^2b^2 + b^4`

Explanation

(i) `a^4 - b^4`

`(a^2)^2 - (b^2)^2`

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

(ii) `p^4 - 81`

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

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

(iii) `x^4 - (y+z)^4`

`(x^2)^2- ((y+z)^2)^2`

...