Simple trigonometry question (help)?

Find the length of the arc on a circle of radius r intercepted by a central angle (theta). Round answer to nearest 2 decimal places.

1. r = 3 meters, (theta) = 75deg

2. r = 55 inches, (theta) = 45deg

I know S=radius(theta), and the degrees *should* translate to 12pi/5 and pi/4 for each, however, when I plug them into the formula, both come out to an answer larger than the circumference. 2pi(3) for instance is 18.8, and 3 x 12pi/5 = 22.6

Where am I going wrong? And what are the correct answers? Please show work.

Seh-Kai Liao2011-08-25T20:22:50Z

Favorite Answer

Just multiply 75 by 3, so 225. Now convert it to radians by multiplying by pi and diving by 180, so

_ 225π / 180

_ 4π /5 = 2.513

12π /5 radians is larger than the circumference because the circumference of the circle would be 2π radians.