Question

Need help with Arc length of polar curve ( urgent!!):
8) Find the length of the curve
r=cos^4 (θ/4)
One loop of the curve r=cos2θ
r=sin(6sinθ)
r=5^θ

For all of them I can't find the limit of integration, I look at the solution and my teacher just says stuff like ( for instance in the 3rd one) from 0< theta < pi... where does she get those from...