# I'm having a hard time factoring this

• Apr 2nd 2009, 06:56 PM
robo_robb
I'm having a hard time factoring this
Hi everyone, I'm trying the find the zeros of the derivative 4x^3 + 9x^2 + 6x +1 so I set it to zero but I am stuck as to how I can factor this. btw the original function is x*(x+1)^2

I've asked a tutor at my school's tutoring center and she said that I should use my calc to find the zeros, which visually look like 1 and ~-2.5.

Any help would be much appreciated!
• Apr 2nd 2009, 07:19 PM
Reckoner
Quote:

Originally Posted by robo_robb
Hi everyone, I'm trying the find the zeros of the derivative 4x^3 + 9x^2 + 6x +1 so I set it to zero but I am stuck as to how I can factor this.

Rational Root Theorem

Synthetic Division
• Apr 2nd 2009, 07:31 PM
robo_robb
That certainly rings a bell. Thank you very much! (Hi)
• Apr 2nd 2009, 08:31 PM
mr fantastic
Quote:

Originally Posted by robo_robb
Hi everyone, I'm trying the find the zeros of the derivative 4x^3 + 9x^2 + 6x +1 so I set it to zero but I am stuck as to how I can factor this. btw the original function is x*(x+1)^2

I've asked a tutor at my school's tutoring center and she said that I should use my calc to find the zeros, which visually look like 1 and ~-2.5.

Any help would be much appreciated!

$y = x (x + 1)^2 = x^3 + 2x^2 + x \Rightarrow \frac{dy}{dx} = 3x^2 + 4x + 1$. There should be no trouble solving $\frac{dy}{dx} = 3x^2 + 4x + 1 = 0$.

I don't see where $y = 4x^3 + 9x^2 + 6x + 1$ fits in .... is this another function for which you have to find the zeros of its derivative? Again, the derivative is a quadratic. and there is no trouble.

Or are you trying to solve $0 = 4x^3 + 9x^2 + 6x + 1$ in which case you note that by inspection $x = -1$ is a solution. Therefore $x + 1$ is a factor. Divide the factor into the cubic to get $(x + 1)(4x^2 + 5x + 1) = 0$. Now solve $4x^2 + 5x + 1 = 0$.
• Apr 2nd 2009, 08:58 PM
robo_robb
Oh I'm sorry, I meant to say x*(x+1)^3

All of the methods posted thus far are a great help. Thanks everyone.

My roots turned out to be -1, -(1/4)