The derivative of the original function is the first derivative, the second derivative and the third derivative of the original function, and so on. The original function can be regarded as a zero-order derivative function.

Let it be f (n) (x), y (n), d (n) y/dx (n), d (n) f (x)/dx (n), where n is the order of the derivative, x is the independent variable, and y=f(x) is a function about x.

For example, the derivative of y = x 2 is y=2x, and the derivative of second derivative y=2x is y=2.

The derivative of y = x 3+3x 2+7x+9 is y = 3x 2+6x+7, the second derivative is y=6x+6 and the third derivative is y=6x+6.