Did you find this equation in an homework? The trick with is a good one, but the equation has no "easy" roots. You can use Cardano's method for instance, which works for any cubic equation. However, you'll probably have to deal with cubic roots of complex numbers, while the three roots are in fact real. I asked Maple (a computer program) for solutions, and for instance one of them can be written as (after manual simplifications of maple's output): ... If this is an homework, I'd bet you made a mistake before. If it is a "real life" problem, use approximate solutions: -0.8957, 0.245, 0.650 for and hence the six square roots (with ) as solutions of the initial equation in , and only four solutions (plus or minus the roots of the two positive roots) in .