Hello, I'm stuck on the following question:

I only get as far as taking natural logs and then differentiation it, but have no idea on how to carry on:

ln(S) = ln(b)+ln(c)+ln(sinA)

Assuming that b and c are equal to 1, I get:

1/S dS = 1/b db + 1/c dc + cot A (sub in [A=pi/4])

That's what I gather from the text book but then I hit dead end.

Any idea on what I'm doing wrong or whether I'm completely wrong from the off?