# C=2 pi r (how do i make 'r' the subject?)

• Dec 5th 2006, 08:17 AM
turbod15b
C=2 pi r (how do i make 'r' the subject?)
c=2 pi r

get rid of r?:confused:
• Dec 5th 2006, 08:45 AM
CaptainBlack
Quote:

Originally Posted by turbod15b
c=2 pi r

get rid of r?:confused:

$\displaystyle c=2\, \pi\, r$

divide both sides by $\displaystyle 2\, \pi$

to get:

$\displaystyle \frac{c}{2\,\pi}=r$,

or:

$\displaystyle r=\frac{c}{2\,\pi}$

RonL
• Dec 5th 2006, 08:53 AM
turbod15b
ty

if pi=3.142 and c=2.84cm

how do i find 'r' ? to 2 significant numbers?

3.142*2.84=8.9?
• Dec 5th 2006, 09:37 AM
topsquark
Quote:

Originally Posted by CaptainBlack
$\displaystyle c=2\, \pi\, r$

divide both sides by $\displaystyle 2\, \pi$

to get:

$\displaystyle \frac{c}{2\,\pi}=r$,

or:

$\displaystyle r=\frac{c}{2\,\pi}$

RonL

Quote:

Originally Posted by turbod15b
ty

if pi=3.142 and c=2.84cm

how do i find 'r' ? to 2 significant numbers?

3.142*2.84=8.9?

Please see CaptainBlack's post.
$\displaystyle r = \frac{c}{2 \pi} = \frac{2.84 \, cm}{2 \cdot 3.142} = 0.45191 \, cm = 0.45 \, cm$

-Dan
• Dec 5th 2006, 10:19 AM
turbod15b
aint it 28.4/(2x3.142)=4.5 > 2 significant numbers

• Dec 5th 2006, 10:28 AM
topsquark
Quote:

Originally Posted by turbod15b
aint it 28.4/(2x3.142)=4.5 > 2 significant numbers