diff --git a/calculus/derivative-rules.md b/calculus/derivative-rules.md index 6731871cf..26bd70170 100644 --- a/calculus/derivative-rules.md +++ b/calculus/derivative-rules.md @@ -1,5 +1,77 @@ # Rules for derivatives +Some useful rules for derivatives to apply are: + +| Rule | $f(x)$ | $f'(x)$ | +|-------------|------------------|----------------------| +| Constant | $k$ | $0$ | +| Power | $x^n$, $n \ne 0$ | $nx^{n-1}$ | +| Multiple | $k u(x)$ | $k u'(x)$ | +| Sum | $u(x) + v(x)$ | $u'(x) + v'(x)$ | +| Difference | $u(x) - v(x)$ | $u'(x) - v'(x)$ | +| Exponential | $a^x$ | $a^x \ln a$ | +| Logarithm | $\log_a x$ | $\dfrac{1}{x \ln a}$ | + +Note that two special cases of the last two derivatives occur when $a = e$: + +\begin{equation} +\dd{}{e^x}{x} = e^x \qquad \dd{}{\ln x}{x} = \frac{1}{x} +\end{equation} + +1. $\displaystyle f(x) = x^3$ + + ```{solution} + \begin{equation} + f'(x) = 3x^{3-1} = 3x^2 + \end{equation} + ``` + +2. $\displaystyle f(x) = -x^2 + 3$ + + ```{solution} + \begin{align} + f'(x) &= \frac{d}{dx}(-x^2) + \frac{d}{dx}(3) \\ + &= -\frac{d}{dx}(x^2) + \frac{d}{dx}(3) \\ + &= -2x^{2-1} + 0 \\ + &= -2x + \end{align} + ``` + +3. $\displaystyle f(x) = \frac{4x^3}{3} - x + 2e^x$ + + ```{solution} + \begin{align} + f'(x) &= \frac{4}{3} \frac{d}{dx}(x^3) - \frac{d}{dx}(x) + + 2 \frac{d}{dx}(e^x) \\ + &= \frac{4}{3}(3x^2) - 1 + 2e^x \\ + &= 4x^2 - 1 + 2e^x + \end{align} + ``` + +4. $\displaystyle f(x) = \frac{3}{x^2} + \sqrt{x}$ + + ```{solution} + \begin{align} + f'(x) &= 3 \frac{d}{dx}(x^{-2}) + \frac{d}{dx}(x^{1/2}) \\ + &= 3(-2x^{-3}) + \frac{1}{2} x^{-1/2} \\ + &= \frac{-6}{x^3} + \frac{1}{2\sqrt{x}} + \end{align} + ``` + +5. $f(x) = \log(4x)$ + + ```{solution} + \begin{align} + f'(x) &= \frac{d}{dx} [\log 4 + \log x] \\ + &= \frac{d}{dx}(\log 4) + \frac{d}{dx}(\log x) \\ + &= 0 + \frac{1}{x \ln 10} + \end{align} + ``` + +There are other rules related to functions that are products, quotients, +compositions, or trigonometric. We will go over each of those in more detail +next. + ## Product rule The product rule is used to differentiate functions that can be written as the