Hi all, I've got a Calculus III Question 1. The problem statement, all variables and given/known data Find the derivative zs and zt, where z=sin(x)cos(2y) 2. Relevant equations x=s+t y=s-t 3. The attempt at a solution I had a go at the solution and this was what I ended up getting for zs, I ended up getting (cosxcos2y)(1)-2sinxsin2y(1) where the 1 at the end of the δx and δy were the partial derivatives of x=s+t and y=s-t I subbed in s and t values for x and y, and I ended up with zs=((cos(s)+cos(t))(cos(2s)-cos(2t)))-((2sin(s)+2sin(t))(sin(2s)-sin(2t))) I did the same process for t and got zt=((-cos(s)-cos(t))(-cos(2s)+cos(2t)))+((2sin(s)+2sin(t))(sin(2s)-sin(2t))) this seems like a really unnecessarily long answer and i'm pretty sure I messed something up. I can't seem to find the mistake though (I have a feeling its right under my nose). Also, I don't know if this is really the easiest way to go about doing these problems. I felt like the past few chapters we've learned in lecture have been kinda rushed. If there is any way where these problems could be solved in an easier way, that advice would be MUCH appreciated. Thanks --my brain feels like its turning into mush P.S. if there are any post-editing mistakes, please forgive me. I am not used to posting on this site yet.