You may want to review solving quadratic equations first.

Sometimes, an equation is really almost quadratic, even though it
doesn't look it. For example, consider
−6*x*^{4} − 3*x*^{2} = 0.
The degree of this equation is 4. But if you look carefully, you
see that only even powers of *x* appear. So we can solve
for *x*^{2}, getting *x*^{2} = 0 or
−1 ⁄ 2. (If you find this confusing,
let's introduce a new variable *y*, where *y*
= *x*^{2}. Then the equation becomes
−6*y*^{2} − 3*y* = 0, and we can
solve for *y*, which is the same thing
as *x*^{2}.) It follows that there are 3
possibilities for *x*: 0, 1 ⁄ 2 *
√2*i* and −1 ⁄ 2 *
√2*i*

This is a somewhat harder idea than most of the ones you've encountered so far. It might take you some time to become comfortable with it.