# Math Help - Finding radius of a circular sector.

1. ## Finding radius of a circular sector.

Find the radius of a circular sector with angle 3π/2

and arc length 3 cm.

I was not there when we did this in class, so I don' know what to do here at all.

2. ## Re: Finding radius of a circular sector.

What would the full arc length of the circle be?

After you know this $C = 2\pi r$

3. ## Re: Finding radius of a circular sector.

Originally Posted by xxStrikeback
Find the radius of a circular sector with angle 3π/2
and arc length 3 cm.
I was not there when we did this in class, so I don' know what to do here at all.
Well you should have been class.
The length of an arc sub-tended by an angle of $\theta$ is $r\theta~.$

4. ## Re: Finding radius of a circular sector.

Originally Posted by Plato
Well you should have been class.
The length of an arc sub-tended by an angle of $\theta$ is $r\theta~.$
Because the proportion of the circle's circumference being measured is $\displaystyle \frac{\theta}{2\pi}$, so the arc length is $\displaystyle \frac{\theta}{2\pi} \times 2\pi r = r\theta$