Question

How do you differentiate `4cos x * sin y = 1`?

Answer 1

Remember the `y` is functin of `x` so:
`4(-sin(x)sin(y))+4cos(x)cos(y)(dy)/(dx)=0`
`(dy)/(dx)=(sin(x)sin(y))/(cos(x)cos(y))=tan(x)tan(y)`