# Partial Derivatives - Chain Rule / Polar Coordinates Problem

(please see image link below) Currently stuck on this problem involving the chain rule and partial derivatives. Having looked at the highlighted part of the solution, I can't figure out two things:

• Surely the $$\sin\psi$$ term should be zero, as it's just taking the partial derivative with respect to $$r$$ of $$\sin\psi$$?
• Likewise, shouldn't the $$r \cos\psi$$ term be simply $$\cos\psi$$, as it's just the partial derivative of $$\sin\psi$$ with respect to $$\psi$$?

Any advice would be much appreciated.

• My immediate advice is to include critical parts of your question as text. Images are neither searchable nor accessible to screen readers, nor do they show up in question summaries. MathJax is used for formatting mathematical expressions here. You can find a quick reference here. – amd May 21 at 19:36
• There’s a typo in the text: it should have $y=r\sin\psi$ instead of $y=\sin\psi$. – amd May 21 at 19:38
• Welcome to Mathematics Stack Exchange! A quick tour will enhance your experience. Here are helpful tips to write a good question and write a good answer. For equations, please use MathJax. – dantopa May 21 at 21:29