# 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:

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

divide both sides by $2\, \pi$

to get:

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

or:

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

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

divide both sides by $2\, \pi$

to get:

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

or:

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

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.
$r = \frac{c}{2 \pi} = \frac{2.84 \, cm}{2 \cdot 3.142} = 0.45191 \, cm = 0.45 \, cm$

-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

(shrugs) You posted "2.84" in your last post. Either way, the problem is done the same way.

I'm not sure, did you have a question about 4.5 having 2 significant figures?

-Dan
• Dec 5th 2006, 11:12 AM
turbod15b
yeh i meant 28.4cm sorry:rolleyes: