,3 y2 aid dy dn

visit the link it might help u to calculate your questions

see this attachment

there is no need of finding the critical points for this question

https://www.emathhelp.net/calculators/calculus-1/implicit-differentiation-calculator/?f=x%5E2%2B2xy%2By%5E3-42&g=0&type=x&px=&py=&steps=on see this link where you can get deri...

see this second derivative

feel any doubt plz ask

if u satisfied with answer then accept it as best answer

pdf file

See this

last step