Question

partial derivative of x cos (yz) WRT z

Answer 1

when you take partial derivative with respect to a variable the other variables are treated as constants so in this case you will need a chain rule
derivtive of cos(yz) wrt z = -sin(wz) now take derivtive of inner, x still stays outside, and get -xwsin(wz) as your partial derivative

Answer 2

thank you!

Answer 3

np glad to help