I've got an expression: $\displaystyle x^4+5x^2+6 $. How can I factorise it? All methods I know are based on finding one solution and simplifying the expression to (x-a)(...). But this one is always positive, no matter x, so it's not possible here. It's a polynomial of degree 4, so it must be possible to at least make it to the form $\displaystyle a(x^2+bx+c)(x^2+dx+e)$ How can I do that? (only real numbers, please)