Given the equation
you should have in mind that the expression x^2-9 and x^3-8 are "numbers" and that the product of two numbers is zero if and only if one of the numbers is zero. Then, by using this, you get the following auxiliary equations
which is equivalent to
so x=3 o x=-3.
Finally, for the other case
So
so the three possible solutions for the equation are x=3, x=-3 and x=2