# Solutions to 4 Degree Polynomial

• Jun 20th 2013, 08:51 PM
ReneG
Solutions to 4 Degree Polynomial
I am trying to compute the solutions to $\mathrm{f(x)} = x^4 + 5x^3 - 9x^2 - 45x$

I factored all the way up to $\mathrm{f(0)} = (x+3)(x-3)(x^2 + 5x)$

Which gave me 3 out of 4 solutions $x = \{-5, -3, 3\}$

My book says the final solution is $0$ but I don't see how they got that.
• Jun 20th 2013, 09:05 PM
MINOANMAN
Re: Solutions to 4 Degree Polynomial
Rene

Factorise the last term x^2+5x =x(x+5) then you will find x = 0 the fourth root...................
the complete factorization is x(x-3)(x+3)(x+5) ...........
• Jun 20th 2013, 09:11 PM
ReneG
Re: Solutions to 4 Degree Polynomial
I'm such a dunce, thanks.