diff --git a/textbook/chainRule/digInChainRule.tex b/textbook/chainRule/digInChainRule.tex index 4cea56807..cd4c0e138 100644 --- a/textbook/chainRule/digInChainRule.tex +++ b/textbook/chainRule/digInChainRule.tex @@ -2,10 +2,20 @@ \input{../preamble.tex} + \outcome{Recognize a composition of functions.} + \outcome{Take derivatives of compositions of functions using the chain rule.} + \outcome{Take derivatives that require the use of multiple derivative rules.} + \outcome{Use the chain rule to calculate derivatives from a table of values.} + \outcome{Understand rate of change when quantities are dependent upon each other.} + \outcome{Use order of operations in situations requiring multiple derivative rules.} + \outcome{Justify the chain rule via the composition of linear approximations.} + \outcome{Apply chain rule to relate quantities expressed with different units.} + \title[Dig-In:]{The chain rule} \begin{document} \begin{abstract} +Here we compute derivatives of compositions of functions \end{abstract} \maketitle @@ -24,7 +34,7 @@ While there are several different ways to differentiate this function, if we let $f(x) = x^5$ and $g(x) = 1+2x$, then we can express $h(x) = -f(g(x))$. The question is, can we compute the derivative of a +\answer[given]{f}(\answer[given]{g}(x))$. The question is, can we compute the derivative of a composition of functions using the derivatives of the constituents $f(x)$ and $g(x)$? To do so, we need the \textit{chain rule}. @@ -186,18 +196,19 @@ \ddx (1+2x)^5 \] - +\begin{explanation} Set $f(x) = x^5$ and $g(x) = 1+2x$, now \[ -f'(x) = 5x^4 \qquad\text{and}\qquad g'(x) = 2. +f'(x) = \answer[given]{5x^4} \qquad\text{and}\qquad g'(x) = \answer[given]{2}. \] Hence \begin{align*} \ddx (1+2x)^5 &= \ddx f(g(x))\\ &=f'(g(x))g'(x) \\ -&= 5(1+2x)^4\cdot 2\\ +&= 5(\answer[given]{1+2x})^4\cdot \answer[given]{2}\\ &= 10(1+2x)^4. \end{align*} +\end{explanation} \end{example} @@ -209,20 +220,21 @@ \ddx \sqrt{1+\sqrt{x}} \] - +\begin{explanation} Set $f(x)=\sqrt{x}$ and $g(x)=1+x$. Hence, \[ -\sqrt{1+\sqrt{x}}=f(g(f(x))) \qquad\text{and}\qquad\ddx f(g(f(x))) = f'(g(f(x)))g'(f(x))f'(x). +\sqrt{1+\sqrt{x}}=f(g(\answer[given]{f}(x))) \qquad\text{and}\qquad\ddx f(g(f(x))) = f'(g(f(x)))g'(f(x))f'(x). \] Since \[ -f'(x) = \frac{1}{2\sqrt{x}} \qquad\text{and}\qquad g'(x) = 1 +f'(x) = \answer[given]{\frac{1}{2\sqrt{x}}} \qquad\text{and}\qquad g'(x) = \answer[given]{1} \] We have that \[ -\ddx \sqrt{1+\sqrt{x}} = \frac{1}{2\sqrt{1+\sqrt{x}}}\cdot 1\cdot \frac{1}{2\sqrt{x}}. +\ddx \sqrt{1+\sqrt{x}} = \frac{1}{2\sqrt{1+\sqrt{x}}}\cdot 1\cdot \answer[given]{\frac{1}{2\sqrt{x}}}. \] +\end{explanation} \end{example} Using the chain rule, the power rule, and the product rule it is @@ -234,19 +246,20 @@ \ddx \frac{x^3}{x^2+1} \] - +\begin{explanation} Rewriting this as \[ \ddx x^3(x^2+1)^{-1}, \] -set $f(x) = x^{-1}$ and $g(x) = x^2+1$. Now +set $f(x) = \answer[given]{x^{-1}}$ and $g(x) = \answer[given]{x^2+1}$ so that $f(g(x)) = (x^2 + 1)^{-1}$. Now \[ -x^3(x^2+1)^{-1} = x^3 f(g(x)) \qquad\text{and}\qquad \ddx x^3 f(g(x)) = 3x^2f(g(x))+ x^3 f'(g(x))g'(x). +x^3(x^2+1)^{-1} = x^3 f(g(x)) \qquad\text{and}\qquad \ddx x^3 f(g(x)) = \answer[given]{3x^2} \cdot f(g(x))+ \answer[given]{x^3} \cdot f'(g(x))g'(x). \] -Since $f'(x) = \frac{-1}{x^2}$ and $g'(x) = 2x$, write +Since $f'(x) = \answer[given]{\frac{-1}{x^2}}$ and $g'(x) = \answer[given]{2x}$, write \[ \ddx \frac{x^3}{x^2+1} = \frac{3x^2}{x^2+1}-\frac{2x^4}{(x^2+1)^2}. \] +\end{explanation} \end{example} \end{document}