Non-real critical values possible?

**beebe** · October 13th 2011, 02:51 PM

The question in question:

Find the critical numbers of the function $f(x)=2x^3+x^2+2x$ .

I know that $f'(x)=6x^2+2x+2=2(3x^2+x+1)$ .

Solving using the quadratic formula gives me $x=\frac{-1\pm\sqrt{11}i}{6}$

I'm only taking Calc 1, so I figured that I should just say that there aren't any critical values, but do non-real values count?

**skeeter** · October 13th 2011, 02:55 PM

Originally Posted by beebe

The question in question:

Find the critical numbers of the function $f(x)=2x^3+x^2+2x$ .

I know that $f'(x)=6x^2+2x+2=2(3x^2+x+1)$ .

Solving using the quadratic formula gives me $x=\frac{-1\pm\sqrt{11}i}{6}$

I'm only taking Calc 1, so I figured that I should just say that there aren't any critical values, but do non-real values count?

not if you're studying calculus of a real variable (which you most probably are)

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