Question

How would i find the length of arc AC when AB is 120 degrees and AC is 90 degrees and the radius is 10?

Answer 1

I found: `s=16`

Explanation:

I am not sure to have interpreted your question right (I do not know why you need AB is 120°..) but anyway:
the length `s` of the arc AC is given as:
`s=r*theta`
where:
`r=10` is the radius;
`theta=90°=pi/2 rad` is the angle.
Using these data in the above expression (the angle has to be in radians) you get:
`s=10*pi/2=5pi=5*3.14=15.7~~16`