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 −6x4 − 3x2 = 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 x2, getting x2 = 0 or −1 ⁄ 2. (If you find this confusing, let's introduce a new variable y, where y = x2. Then the equation becomes −6y2 − 3y = 0, and we can solve for y, which is the same thing as x2.) It follows that there are 3 possibilities for x: 0, 1 ⁄ 2 * √2i and −1 ⁄ 2 * √2i
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.