How do you find the radius of a sector?

If we know the area of the sector (A) and Θ, we can use

A = (1/2)r²Θ

So...... r² = 2A/Θ     .....and taking the positive root of both sides, we have

r =√(2A/Θ)

If we know the arc length (s) and Θ, we can use

s =rΘ

So r = s/Θ

The radius of the sector is the radius of the circle.

Do you know the area of the sector? the area of the circle?

I would need to know more information before I can answer this question; can you send more information?