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

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

c=2 pi r

get rid of r?

2. Originally Posted by turbod15b
c=2 pi r

get rid of r?
$\displaystyle c=2\, \pi\, r$

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

to get:

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

or:

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

RonL

3. ty

if pi=3.142 and c=2.84cm

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

3.142*2.84=8.9?

4. 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
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?
$\displaystyle r = \frac{c}{2 \pi} = \frac{2.84 \, cm}{2 \cdot 3.142} = 0.45191 \, cm = 0.45 \, cm$

-Dan

5. aint it 28.4/(2x3.142)=4.5 > 2 significant numbers

6. 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

7. yeh i meant 28.4cm sorry