Question 282094
Rewrite as:

{{{(x^2)^2-(7x)^2=0}}}
Use difference of squares formula.
{{{(x^2+7x)(x^2-7x)=0}}}
So we want:
x^2+7x=0 or x^2-7x=0
ie:
x(x+7)=0 or x(x-7)=0
x=-7 or 0; or x=7 or 0


Hence we have solution set {-7,0,7} with 0 occurring twice.