Product rule
With the product rule you can calculate the derivative of a product of two functions
This formula is stated quite unclear.
Explanation
We start with the functions f (x) en g (x). In the definition of the derivative we substitute these functions
By adding and subtraction the term in the numerator we get
The limit of a sum is the sum of the limits, so
As h→0 the two fractions describe the derivatives f ′(x) and g ′(x). The function f (x) is differentiable, so f (x + h) → f (x)
You can guess what the product of 3 functions will look like.