Function of a Function
Suppose y is a function of z,
y = f(z)
and z is a function of x,
z = g(x)
Since, y depends on z, and z in turn depends on x, y is also a function of x.
Thus, y = f(z)
The derivative of y with respect to x can be obtained as:
The above method is often used to get the derivative of some complicated functions.