You may want to review solving quadratics in x2 first.
The same thing works even if, instead of x2 or x3 as the thing we're solving for, we have x raised to a fractional power. The one trick here is that even roots of x, like x1 ⁄ 2 or x1 ⁄ 4, are always positive or 0. So, if the Quadratic Formula gives you any negative solutions, you should ignore them. Otherwise, it's the same as before. (Now, of course, to get x, you'll need to raise to a power instead of taking a root.)