# Thread: am i being stupid?

1. ## am i being stupid?

I have this:

-6 + Sqrt 6^2 - 4*1*6
2*1

so following this through i ended up at:

-3 + Sqrt 6

but the answer in my book is saying i should have the square root of 3.
How does square root of 12 divided by 2 end up as square root of 3 instead of 6 (12/2)??

probably really simple but after reading about eigenvalues and dynamic matrix for the last hour my heads just hurts......

2. Originally Posted by thermalwarrior
I have this:

-6 + Sqrt 6^2 - 4*1*6
2*1

so following this through i ended up at:

-3 + Sqrt 6

but the answer in my book is saying i should have the square root of 3.
How does square root of 12 divided by 2 end up as square root of 3 instead of 6 (12/2)??

probably really simple but after reading about eigenvalues and dynamic matrix for the last hour my heads just hurts......
$\displaystyle \frac{-6 \pm \sqrt{6^2 - (4)(1)(6)}}{(2)(1)}$

$\displaystyle \frac{-6 \pm \sqrt{12}}{2}$

$\displaystyle \frac{-6 \pm \sqrt{(4)(3)}}{2}$

$\displaystyle \frac{-6 \pm \sqrt{(4)}\sqrt{(3)}}{2}$

$\displaystyle \frac{-6 \pm 2 \sqrt{(3)}}{2}$

$\displaystyle -3 \pm \sqrt{3}$

3. what an incredible ***** !