Question

solve ( x power 4 ) -81

Answer 1

$x^{4} - 81$
$= (x^{2})^{2} - 9^{2}$
$= (x^{2}-9)(x^{2}+9)$
$= (x-3)(x+3)(x^{2}+9)$

Hope this may help you. 

Answer 2

(x power 4)-81=0
(x power 4)=81
x=fourth root of 81 (i.e.,⁴√81)
that is equal to 3
.: x = 3