**Introduction:**In Chapter 2 the derivative of a function of one variable is discussed.

**Definition:**Let $y(x)$ be a function of one variable. Then the derivative of the derivative $y'(x)$ is called the

*second-order*

*derivative*of $y(x)$. The second-order derivative is denoted as $y''(x)$.

**Remark:**The second-order derivative can be determined from the first-order derivative by the usual rules of differentiation.