SOLUTION: x^3 + 5x^2 - 4x - 20 = 0 i know that's the cubic equation, but i seriously can't find a good equation to find the roots. I NEED HELP! x^4 + 9x^3 + 18x^2 = 0 i know this is a q

Algebra ->  Polynomials-and-rational-expressions -> SOLUTION: x^3 + 5x^2 - 4x - 20 = 0 i know that's the cubic equation, but i seriously can't find a good equation to find the roots. I NEED HELP! x^4 + 9x^3 + 18x^2 = 0 i know this is a q      Log On


   

Question 329908: x^3 + 5x^2 - 4x - 20 = 0
i know that's the cubic equation, but i seriously can't find a good equation to find the roots. I NEED HELP!
x^4 + 9x^3 + 18x^2 = 0
i know this is a quartic trinomial, but i don't know how to solve this and the paper expects 4 roots.
(3x + 1)(2x + 7) = 0
i think i set these equal to zero, but am i supposed to get a fraction?
Answer by scott8148(6628) About Me  (Show Source):
You can put this solution on YOUR website!
grouping ___ (x^3 + 5x^2) - (4x + 20)

factoring ___ x^2(x + 5) - 4(x + 5)

rearranging ___ (x^2 - 4)(x + 5)

factoring (difference of squares) ___ (x + 2)(x - 2)(x + 5)


factoring ___ x^2(x^2 + 9x +18) = 0

factoring again ___ (x)(x)(x + 6)(x + 3) = 0 ___ x = 0 is a double root


roots do NOT have to be whole numbers (or rational , for that matter)