diff --git a/quarto/derivatives/derivatives.qmd b/quarto/derivatives/derivatives.qmd index 7df39ca..8c10e94 100644 --- a/quarto/derivatives/derivatives.qmd +++ b/quarto/derivatives/derivatives.qmd @@ -515,7 +515,7 @@ This example shows a useful template: \begin{align*} -[2x^2 - \frac{x}{3} + 3e^x]' & = 2[\square]' - \frac{[\square]]}{3} + 3[\square]'\\ +[2x^2 - \frac{x}{3} + 3e^x]' & = 2[\square]' - \frac{[\square]'}{3} + 3[\square]'\\ &= 2[x^2]' - \frac{[x]'}{3} + 3[e^x]'\\ &= 2(2x) - \frac{1}{3} + 3e^x\\ &= 4x - \frac{1}{3} + 3e^x @@ -552,7 +552,7 @@ This example shows a useful template for the product rule: ### Quotient rule -The derivative of $f(x) = u(x)/v(x)$ - a ratio of functions - can be similarly computed. The result will be $[u/v]' = (u'v - uv')/u^2$: +The derivative of $f(x) = u(x)/v(x)$ - a ratio of functions - can be similarly computed. The result will be $[u/v]' = (u'v - uv')/v^2$: ```{julia} @@ -609,7 +609,7 @@ The same $u$ and $v$ my be identified. The quotient rule readily applies to yiel $$ -f'(x) = u'v - uv' = \frac{\cos(x) \cdot (1 + x^2) - (1 + \sin(x)) \cdot (2x)}{(1+x^2)^2}. +f'(x) = \frac{u'v - uv'}{v^2} = \frac{\cos(x) \cdot (1 + x^2) - (1 + \sin(x)) \cdot (2x)}{(1+x^2)^2}. $$ --- @@ -653,7 +653,7 @@ This pattern generalizes, clearly, to: $$ -[f_1\cdot f_2 \cdots f_n]' = f_1' f_2 \cdots f_n + f_1 \cdot f_2' \cdot (f_3 \cdots f_n) + \dots + +[f_1\cdot f_2 \cdots f_n]' = f_1' f_2 \cdots f_n + f_1 \cdot f_2' \cdot f_3 \cdots f_n + \dots + f_1 \cdots f_{n-1} \cdot f_n'. $$ @@ -777,14 +777,14 @@ $$ --- -Find the derivative of $\log(2 + \sin(x))$. This is a composition $\log(x)$ – with derivative $1/x$ and $2 + \sin(x)$ – with derivative $\cos(x)$. We get $(1/\sin(x)) \cos(x)$. +Find the derivative of $\log(2 + \sin(x))$. This is a composition $\log(x)$ – with derivative $1/x$ and $2 + \sin(x)$ – with derivative $\cos(x)$. We get $(1/(2 + \sin(x))) \cos(x)$. In general, $$ -[\log(f(x))]' \frac{f'(x)}{f(x)}. +[\log(f(x))]' = \frac{f'(x)}{f(x)}. $$ --- @@ -835,8 +835,8 @@ Rearranging: $$ -f(g(a+h)) - f(g(a)) - f'(g(a)) g'(a) h = f'(g(a))\epsilon_g(h))h + \epsilon_f(h')(h') = -(f'(g(a)) \epsilon_g(h) + \epsilon_f(h')( (g'(a) + \epsilon_g(h))))h = +f(g(a+h)) - f(g(a)) - f'(g(a)) g'(a) h = f'(g(a))\epsilon_g(h)h + \epsilon_f(h')(h') = +(f'(g(a)) \epsilon_g(h) + \epsilon_f(h') (g'(a) + \epsilon_g(h)))h = \epsilon(h)h, $$ @@ -846,7 +846,7 @@ where $\epsilon(h)$ combines the above terms which go to zero as $h\rightarrow 0 ##### The "chain" rule -The chain rule name could also be simply the "composition rule," as that is the operation the rule works for. However, in practice, there are usually *multiple* compositions, and the "chain" rule is used to chain together the different pieces. To get a sense, consider a triple composition $u(v(w(x())))$. This will have derivative: +The chain rule name could also be simply the "composition rule," as that is the operation the rule works for. However, in practice, there are usually *multiple* compositions, and the "chain" rule is used to chain together the different pieces. To get a sense, consider a triple composition $u(v(w(x)))$. This will have derivative: @@ -1318,7 +1318,7 @@ Compute the derivative of $x^e$ using `limit`. What do you get? #| hold: true #| echo: false choices = ["``e^x``", "``x^e``", "``(e-1)x^e``", "``e x^{(e-1)}``", "something else"] -answ = 5 +answ = 4 radioq(choices, answ, keep_order=true) ``` @@ -1418,7 +1418,7 @@ Consider the function $f$ and its transformation $g(x) = f(x - a)$ (shift right yesnoq("no") ``` -Consider the function $f$ and its transformation $g(x) = f(x - a)$ (shift right by $a$). Is $f'$ at $x$ equal to $g'$ at $x-a$? +Consider the function $f$ and its transformation $g(x) = f(x - a)$ (shift right by $a$). Is $g'$ at $x$ equal to $f'$ at $x-a$? ```{julia} @@ -1511,7 +1511,7 @@ answ = 3 radioq(choices, answ) ``` -##### Question +###### Question Their are $6$ trig functions. The derivatives of $\sin(x)$ and $\cos(x)$ should be memorized. The others can be derived if not memorized using the quotient rule or chain rule. @@ -1531,7 +1531,7 @@ trig_choices = [ radioq(trig_choices, 1) ``` -What is $[\cot(x)]'$? (Use $\tan(x) = \cos(x)/\sin(x)$.) +What is $[\cot(x)]'$? (Use $\cot(x) = \cos(x)/\sin(x)$.) ```{julia} @@ -1555,7 +1555,7 @@ What is $[\csc(x)]'$? (Use $\csc(x) = 1/\sin(x)$.) radioq(trig_choices, 4) ``` -##### Question +###### Question Consider this picture of composition: @@ -1598,9 +1598,8 @@ Assuming the approximation gets better for $h$ close to $0$, as it visually does \begin{align*} \frac{d(f\circ g)}{dx}\mid_{x=1} &= \lim_{h\rightarrow 0} \frac{f(g(1) + g'(1)h)-f(g(1))}{h}\\ -&= \lim_{h\rightarrow 0} \frac{f(g(1) + g'(1)h)-f(g(1))}{h}\\ &= \lim_{h\rightarrow 0} \frac{f(g(1) + g'(1)h)-f(g(1))}{g'(1)h} \cdot g'(1)\\ -&= \lim_{h\rightarrow 0} (f\circ g)'(1) \cdot g'(1). +&= \lim_{h\rightarrow 0} (f\circ g)'(g(1)) \cdot g'(1). \end{align*}