How would I find the radius of a circle knowing its radian measure and area of the sector?

Question

Q: An arc on a circle subtends a central angle of θ=4 radians, and the area of the sector is 128 cm2. Determine the radius, r centimeters, of the circle.

 

I know the formula is A= .5 x theta x r^2 but I'm unsure how to go about solving this. I've tried several different things and my homework is online and keeps saying it's incorrect. Thanks for any help you can provide!

Answer 1

you have the formula and the area and the theta.

 

½θr² = 128;  since one half of 4 radians is 2,

 

2r² = 128  so r² = 64  so  r = 8 cm.