Partial derivatives with constrained variables

[jimbo71]

Homework Statement

x^2+y^2=r^2
y-rcos(pheta)
find (partialy/partialr)subscribt phetal, find (partialy/partialpheta)subscribtx, and find (partialy/partial)subsribt pehta

Homework Equations

im not sure how to write this partial in chain rule form. i think the first one (partialy/partialr)subscritpheta would simply be cos(pheta). however i have no idea how to write out the chair rule forumulas for the second and third one. please help

The Attempt at a Solution

 

[jimbo71]

please help asap !