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94 changes: 44 additions & 50 deletions ptx/sec_deriv_basic_rules.ptx
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<title>Derivatives of Common Functions</title>
<statement>
<p>
<dl>
<li>
<ol cols="2">
<li xml:id="constant-derivative-rule">
<title>Constant Rule</title>

<idx><h>derivative</h><h>Constant Rule</h></idx>
<idx><h>derivative</h><h>Constant Rule</h></idx>

<p>
<m>\lzoo{x}{c} = 0</m>, where <m>c</m> is a constant.
</p>
</li>

<li xml:id="power-derivative-rule">
<title>Power Rule</title>

<title>Power Rule</title>
<idx><h>derivative</h><h>Power Rule</h></idx>
<idx><h>Power Rule</h><h>differentiation</h></idx>

Expand All @@ -73,26 +71,27 @@
where <m>n</m> is an integer, <m>n \gt 0</m>.
</p>
</li>

<li>
<title>Other common functions</title>
<p>
<m>\lzoo{x}{\sin(x)} = \cos(x)</m>
</p>

</li>
<li>
<p>
<m>\lzoo{x}{\cos(x)} = {-\sin(x)}</m>
</p>

</li>
<li>
<p>
<m>\lzoo{x}{e^x} = e^x</m>
</p>

</li>
<li>
<p>
<m>\lzoo{x}{\ln(x)} = \frac{1}{x}</m>, for <m>x \gt 0</m>.
</p>
</li>
</dl>
</ol>

<idx><h>derivative</h><h>basic rules</h></idx>

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</ol>
</p>

<figure xml:id="fig_xcubedwithderiv" vshift="-1">
<caption>A graph of <m>f(x) = x^3</m>, along with its derivative <m>\fp(x) = 3x^2</m> and its tangent line at <m>x=-1</m></caption> <!-- START figures/fig_xcubedwithderiv.tex -->
<figure xml:id="fig_xcubedwithderiv" vshift="3">
<caption>A graph of <m>f(x) = x^3</m>, along with its derivative <m>\fp(x) = 3x^2</m> and its tangent line at <m>x=-1</m></caption>
<!-- START figures/fig_xcubedwithderiv.tex -->
<image width="47%">
<shortdescription>
Graph of function x^3, its derivative and a tangent line drawn at point (-1,-1).
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The following theorem helps with the first two of these examples
(the third is answered in the next section).
</p>

<theorem xml:id="thm_deriv_prop">
<title>Properties of the Derivative</title>
<statement>
<p>
Let <m>f</m> and <m>g</m> be differentiable on an open interval <m>I</m> and let <m>c</m> be a real number.
Let <m>f</m> and <m>g</m> be differentiable on an open interval
<m>I</m> and let <m>c</m> be a real number.
Then:
<dl>
<ol cols="1">
<li xml:id="sum-difference-derivative-rule">
<title>Sum/Difference Rule</title>
<p>
<md>
<mrow>\lzoo{x}{f(x) \pm g(x)} \amp= \lzoo{x}{f(x)} \pm \lzoo{x}{g(x)}</mrow>
<mrow>\amp= \fp(x)\pm g'(x)</mrow>
</md>

<p>
<me>\lzoo{x}{f(x) \pm g(x)} = \lzoo{x}{f(x)} \pm \lzoo{x}{g(x)}
=\fp(x)\pm g'(x)
</me>
<idx><h>derivative</h><h>Sum/Difference Rule</h></idx>
<idx><h>Sum/Difference Rule</h><h>of derivatives</h></idx>

Expand All @@ -311,20 +310,18 @@
<li xml:id="constant-multiple-derivative-rule">
<title>Constant Multiple Rule</title>
<p>
<md>
<mrow>\lzoo{x}{c\cdot f(x)} \amp= c\cdot\lzoo{x}{f(x)}</mrow>
<mrow>\amp = c\cdot\fp(x)</mrow>
</md>.

<me>
\lzoo{x}{c\cdot f(x)} =c\cdot\lzoo{x}{f(x)}=c\cdot\fp(x)
</me>
<idx><h>derivative</h><h>Constant Multiple Rule</h></idx>
<idx><h>Constant Multiple Rule</h><h>of derivatives</h></idx>

</p>
</li>
</dl>
</ol>
</p>
</statement>
</theorem>
</theorem>

<figure xml:id="vid_deriv_basic_rules_const_sum_rule" component="video" vshift="2">
<caption>Video presentation of <xref ref="thm_deriv_prop"/></caption>
Expand All @@ -343,6 +340,7 @@
<video youtube="nVVpyilxZTw" label="vid_deriv_basic_rules_proofs"/>
</figure>

<pagebreak-latex/>

<p>
<xref ref="thm_deriv_prop"/>
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<subsection>
<title>Higher Order Derivatives</title>
<aside xml:id="aside-derivative-second-order-notation" vshift="2">
<p>
<em>Note:</em> The second derivative notation could be written as
<me>
\frac{d^2y}{dx^2}=\frac{d^2y}{(dx)^2}=\frac{d^2}{(dx)^2}\big(y\big)
</me>.
</p>

<p>
That is, we take the derivative of <m>y</m> twice
(hence <m>d^2</m>),
both times with respect to <m>x</m> (hence <m>(dx)^2=dx^2</m>).
</p>
</aside>

<p>
The derivative of a function <m>f</m> is itself a function,
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</statement>
</definition>

<aside xml:id="aside-derivative-second-order-caveat" vshift="6">
<title>Higher Order Derivative Caveat</title>
<aside xml:id="aside-derivative-second-order-caveat" vshift="4">
<title>Higher Order Derivative Notes <!-- Caveat --></title>
<p>
<xref ref="def_Higher_Deriv"/>
comes with the caveat <q>Where the corresponding limits exist.</q>
With <m>f</m> differentiable on <m>I</m>,
it is possible that <m>\fp</m> is <em>not</em>
differentiable on all of <m>I</m>, and so on.
</p>
<p>
Also, the second derivative notation could be written as
<me>
\frac{d^2y}{dx^2}=\frac{d^2y}{(dx)^2}=\frac{d^2}{(dx)^2}\big(y\big)
</me>.
That is, we take the derivative of <m>y</m> twice
(hence <m>d^2</m>),
both times with respect to <m>x</m> (hence <m>(dx)^2=dx^2</m>).
</p>
</aside>

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<li><m>f(x) = \sin(x)</m></li>
<li><m>f(x) = 5e^x</m></li>
</ol>
</p>
</p>
</statement>

<pagebreak-latex/>

<solution>
<p>
<ol>
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What do higher order derivatives <em>mean</em>?
What is the practical interpretation?

<!-- TODO: is ! the right markup here? -->

<idx><h>derivative</h><h>higher order!interpretation</h></idx>
<idx><h>derivative</h><h>higher order</h><h>interpretation</h></idx>
</p>

<p>
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57 changes: 26 additions & 31 deletions ptx/sec_deriv_chainrule.ptx
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Expand Up @@ -40,7 +40,7 @@
So it can't be correct to say that <m>y'=-\sin(2x)</m>.
</p>

<figure xml:id="fig_chain" vshift="-4">
<figure xml:id="fig_chain" vshift="0">
<caption>A graph of <m>y=\cos(x^2)</m> and a tangent line at <m>\pi/2</m></caption>
<image width="47%">
<shortdescription>
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</solution>
</example>

<aside vshift="0">
<aside vshift="-3">
<p>
When composing functions,
we need to make sure that the new function is actually defined.
Expand All @@ -166,7 +166,7 @@

<p>
The statement of <xref ref="thm_chain_rule"/> takes care to ensure
this problem does not arise, but our focus is more on the derivative result than
this problem does not arise. We will focus more on the derivative result than
on the domain/range conditions.
</p>
</aside>
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The tangent line is sketched along with <m>f</m> in <xref ref="fig_chain7"/>.
</p>

<figure xml:id="fig_chain7" vshift="0">
<figure xml:id="fig_chain7" vshift="2.5">
<caption><m>f(x) = \cos(x^2)</m> sketched along with its tangent line at <m>x=1</m></caption>
<!-- START figures/fig_chain7.tex -->
<image width="47%">
Expand Down Expand Up @@ -832,32 +832,7 @@
That is, the rate at which the <m>u</m> gear makes a revolution is twice as fast as the rate at which the <m>x</m> gear makes a revolution.
</p>

<sidebyside widths="47% 47%" margins="0%">

<stack><!-- Old paragraphs title: -->
<p>
Using the terminology of calculus,
the rate of <m>u</m>-change, with respect to <m>x</m>,
is <m>\lz{u}{x} = 2</m>.
</p>

<p>
Likewise, every revolution of <m>u</m> causes <m>3</m> revolutions of <m>y</m>:
<m>\lz{y}{u} = 3</m>.
How does <m>y</m> change with respect to <m>x</m>?
For each revolution of <m>x</m>,
<m>y</m> revolves <m>6</m> times; that is,
<me>
\frac{dy}{dx} = \frac{dy}{du}\cdot \frac{du}{dx} = 2\cdot 3 = 6
</me>.
</p>

<p>
We can then extend the <xref ref="thm_chain_rule" text="title"/> with more variables by adding more gears to the picture.
</p>
</stack>

<figure xml:id="fig_chainrulegears">
<figure xml:id="fig_chainrulegears" vshift="0">
<caption>A series of gears to demonstrate the Chain Rule. Note how <m>\lz{y}{x} = \lz{y}{u}\cdot\lz{u}{x}</m></caption>
<!-- START figures/fig_chainrule_gears.tex -->
<image>
Expand Down Expand Up @@ -915,7 +890,27 @@
</image>
<!-- figures/fig_chainrule_gears.tex END -->
</figure>
</sidebyside>

<p>
Using the terminology of calculus,
the rate of <m>u</m>-change, with respect to <m>x</m>,
is <m>\lz{u}{x} = 2</m>.
</p>

<p>
Likewise, every revolution of <m>u</m> causes <m>3</m> revolutions of <m>y</m>:
<m>\lz{y}{u} = 3</m>.
How does <m>y</m> change with respect to <m>x</m>?
For each revolution of <m>x</m>,
<m>y</m> revolves <m>6</m> times; that is,
<me>
\frac{dy}{dx} = \frac{dy}{du}\cdot \frac{du}{dx} = 2\cdot 3 = 6
</me>.
</p>

<p>
We can then extend the <xref ref="thm_chain_rule" text="title"/> with more variables by adding more gears to the picture.
</p>

<p>
It is difficult to overstate the importance of the <xref ref="thm_chain_rule" text="title"/>.
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