Question

find derivative of 4cos(2x)sin(y)=7

Answer 1

I didn't get that result, but something similar.

Answer 2

Let me know if you are still unclear.

Answer 3

\[4\cos(2x)\sin(y)=7\\
\sin(y)= {7\over 4}\sec(2x) \\
\cos(y){dy\over dx}={7\over 4}\times2\times\tan(2x)\sec(2x)\\
{dy\over dx} ={7\over 2}\tan(2x)\sec(2x)\sec(y)\\
\]