Question

what is dy/ dx equal to

Answer 1

dy/dx gives the derivative of y with respect to x.
In a standard curve y=f(x), dy/dx gives the slope of the curve at any point x.

Answer 2

it gives derivative of y with respect to x.
for example:::d(sin x)/dx is equal to cos x.
                   but if we write d(sin y)/dx then it is equal to cos y dy/dx.