# formulas and solving equations

• Sep 1st 2007, 11:27 AM
bobbie bruce
formulas and solving equations

how can i rearrange formula for r in terms of v and h

no good at trigonometry. anybody help with simple explanations:confused:
• Sep 1st 2007, 11:31 AM
red_dog
$\displaystyle \displaystyle V=\frac{\pi r^2h}{3}$
Now solve for $\displaystyle r$
• Sep 2nd 2007, 05:05 AM
bobbie bruce
Quote:

Originally Posted by red_dog
$\displaystyle \displaystyle V=\frac{\pi r^2h}{3}$
Now solve for $\displaystyle r$

thanks red dog but can you simplify it. my old brain doesnt understand the lingo
• Sep 2nd 2007, 05:12 AM
earboth
Quote:

Originally Posted by bobbie bruce

how can i rearrange formula for r in terms of v and h

no good at trigonometry. anybody help with simple explanations:confused:

Hello,

I start at: $\displaystyle V_{cone}=\frac{1}{3} \cdot \pi \cdot r^2 \cdot h$

Multiply both sides by 3:

$\displaystyle 3V = \pi \cdot r^2 \cdot h$ Divide by $\displaystyle (\pi \cdot h)$ :

$\displaystyle \frac{3V}{\pi \cdot h} = r^2$ Calculate the square-root:

$\displaystyle \sqrt{\frac{3V}{\pi \cdot h}} = r$ ... and here you are.