How can I find the roots of these equations. I.E, how can I factor the cubic to get a binomial and a quadratic so then I can use the quad. formula for the last two factors?

TYIA

$\displaystyle 10x^3-x^2+5x+4=0$

also

$\displaystyle 3x^4+2x^3+7x^2+8x-20=0$