second derivative of siny+cosy=x?

Thanks, but I am really looking for a full answer and not just instructions. ^

But people here on TSR want to help you learn not just do the work for you, that means nudging you in the right direction. I'd suggest you take the hints and try and work through it.

Apologies, my intentions were not to come across as unappreciative, but the truth is that I have pretty much exhausted my thought and am consistently getting very similar but different answers.

Sometimes, it is easier to see how other people work things out and then adjust your method.

Thank-you either way.