Attached above is the question that I'm struggling with, specifically part b. I was able to get the gradient as 12si + 10tj, however I don't know to find the point where the gradient vanishes. Can someone please explain to me what are the next steps, without telling me the answer, so that I am able to solve part b
If the gradient is $u(s,t)i+v(s,t)j$, then the gradient vanishes when $u(s,t)=0$ and $v(s,t)=0$.
Solve for $s$ and $t$.
Edit:
\begin{align}f(s,t)&=(1-s-4)^2+(1+s-1-t)^2+(2-2s-2t)^2\\ &=(3+s)^2 +(s-t)^2+(2-2s-2t)^2 \end{align}
Can you use chain rule rule to differetiate with respect to $s$?
Can you use chain rule to differentiate with respect to $t$?