# Math Help - help find critical points/good one

1. ## help find critical points/good one

I am working a problem on mathlab. It looks straightforward until I apply the quadratic formula and I get a negative number under a square root, which isn't allowed.

Locate the critical points of the function $f(x)=x^3+4x^2+9x+1$

the derivative is $f'=3x^2+8x+9$

Critical points are when F'=0, so I apply the quadratic formula to find the CP's.

$\frac{-(8) + or - \sqrt{8^2 - 4(3)(9)}}{2(3)}$

this will simply to
$\frac{-8+ \sqrt{-44}}{6}$ and $\frac{-8-\sqrt{-44}}{6}$
The negative number in the sqrt doesn't make sense.

2. ## Re: help find critical points/good one

it does make sense ... the original function has no critical values. What does that tell you?

3. ## Re: help find critical points/good one

That there is no local maxima or minima