An Introduction to Econometric Theory

CEssential Calculus

The derivative of a function at a point , when defined, is the tangent to the function at . Formally

The function is said to be ‘differentiable at ’ if the limit exists and takes the same value for and . The derivative at is also written for brevity as .

Rules for differentiation include the following:

1. Function rules:
   1. If ,
   2. If ,
   3. If ,
2. Linear rule: , and constants.
3. Product rule: .
4. Quotient ...