Question

at the end of lecture 17, when talking about rotating around a point on circumference, Professor Aroux set the inner upper limit to be 2acos(angle), but why not just 2a?
Thanks

Answer 1

Because that limit is varying, as you can notice, when you take, for example, a/2 in the x axis, the distance between the origin and "r" is different than the distance when you take x=2a.

Answer 2

oh, thanks