Supremum

**Showcase_22** · November 2nd 2008, 09:20 AM

$Sup {x \in \Re: x^2+4x+1<0}$

I'm not sure how to get the set brackets up so here it is without the math bits next to it:

Sup {x \in \Re: x^2+4x+1<0}

What's the answer?

**Plato** · November 2nd 2008, 09:40 AM

Did you graph $x^2 +4x +1$ ?
What is the larger of the two roots?

**Showcase_22** · November 2nd 2008, 11:35 PM

Well I can use the quadratic formula to get $\frac{-4 + \sqrt {4^2-4}}{{2}}=\frac{-4 + \sqrt{12}}{2}=\frac{-4 + 2 \sqrt 2}{2}=-2+\sqrt 2$ .

I was just thinking that the answer would be zero since the greatest value of $x^2+4x+1$ is 0. I can see what I was doing wrong now.

cheers!

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