I'm getting thrown off by the ∂γ/∂s in ∂σ/∂s and also the fact that there is an addition in both ∂σ/∂s and ∂σ/∂v.

I am aware n and b are the normal and binormal, and thus throwing an scalar constant r and cos/sin in front still makes them vectors, but I don't know how to deal with the additions!

Would greatly appreciate some advice as to how to tackle them!