$f{(x)}$ and $g{(x)}$ are two differential functions in terms of $x$. The quotient of them is written as $\dfrac{f{(x)}}{g{(x)}}$ in mathematics and the derivative of quotient of them with respect to $x$ is written in the following mathematical form.
$\dfrac{d}{dx}{\, \Bigg(\dfrac{f{(x)}}{g{(x)}}\Bigg)}$
Take $q{(x)} = \dfrac{f{(x)}}{g{(x)}}$
$\implies$ $\dfrac{d}{dx}{\, \Bigg(\dfrac{f{(x)}}{g{(x)}}\Bigg)}$ $\,=\,$ $\dfrac{d}{dx}{\, q{(x)}}$
According to the definition of the derivative, the derivative of the quotient of two differential functions can be written in the form of limiting operation for finding the differentiation of quotient by first principle.
$\dfrac{d}{dx}{\, q{(x)}}$ $\,=\,$ $\displaystyle \large \lim_{\Delta x \,\to\, 0}{\normalsize \dfrac{q{(x+\Delta x)}-q{(x)}}{\Delta x}}$
Take $\Delta x = h$ and replace the $\Delta x$ by $h$ in the right-hand side of the equation.
$\implies$ $\dfrac{d}{dx}{\, q{(x)}}$ $\,=\,$ $\displaystyle \large \lim_{h \,\to\, 0}{\normalsize \dfrac{q{(x+h)}-q{(x)}}{h}}$
We have taken that $q{(x)} = \dfrac{f{(x)}}{g{(x)}}$, then $q{(x+h)} = \dfrac{f{(x+h)}}{g{(x+h)}}$. Now, replace the functions $q{(x+h)}$ and $q{(x)}$ by their actual values.
$\implies$ $\dfrac{d}{dx}{\, \Bigg(\dfrac{f{(x)}}{g{(x)}}\Bigg)}$ $\,=\,$ $\displaystyle \large \lim_{h \,\to\, 0}{\normalsize \dfrac{\dfrac{f{(x+h)}}{g{(x+h)}}-\dfrac{f{(x)}}{g{(x)}}}{h}}$
$=\,\,\,$ $\displaystyle \large \lim_{h \,\to\, 0}{\normalsize \dfrac{\dfrac{{f{(x+h)}}{g{(x)}}-{g{(x+h)}}{f{(x)}}}{{g{(x+h)}}{g{(x)}}}}{h}}$
$=\,\,\,$ $\displaystyle \large \lim_{h \,\to\, 0}{\normalsize \dfrac{{f{(x+h)}}{g{(x)}}-{g{(x+h)}}{f{(x)}}}{h \times {g{(x+h)}}{g{(x)}}}}$
Now, add and subtract $f{(x)}g{(x)}$ in the numerator of the function for factoring the mathematical expression.
$\implies$ $\dfrac{d}{dx}{\, \Bigg(\dfrac{f{(x)}}{g{(x)}}\Bigg)}$ $\,=\,$ $\displaystyle \large \lim_{h \,\to\, 0}{\normalsize \dfrac{{f{(x+h)}}{g{(x)}}-{g{(x+h)}}{f{(x)}}+{f{(x)}}{g{(x)}}-{f{(x)}}{g{(x)}}}{h \times {g{(x+h)}}{g{(x)}}}}$
$=\,\,\,$ $\displaystyle \large \lim_{h \,\to\, 0}{\normalsize \dfrac{{f{(x+h)}}{g{(x)}}-{f{(x)}}{g{(x)}}-{g{(x+h)}}{f{(x)}}+{f{(x)}}{g{(x)}}}{h \times {g{(x+h)}}{g{(x)}}}}$
In the numerator, $g{(x)}$ is a common factor in the first two terms and $f{(x)}$ is a common factor in the remaining two terms. So, take them common to take a first step in simplifying this mathematical expression.
$\implies$ $\dfrac{d}{dx}{\, \Bigg(\dfrac{f{(x)}}{g{(x)}}\Bigg)}$ $\,=\,$ $\displaystyle \large \lim_{h \,\to\, 0}{\normalsize \dfrac{{g{(x)}}\Big(f{(x+h)}-f{(x)}\Big)-{f{(x)}}\Big(g{(x+h)}-g{(x)}\Big)}{h \times {g{(x+h)}}{g{(x)}}}}$
$=\,\,\,$ $\displaystyle \large \lim_{h \,\to\, 0}{\normalsize \Bigg[\dfrac{{g{(x)}}\Big(f{(x+h)}-f{(x)}\Big)-{f{(x)}}\Big(g{(x+h)}-g{(x)}\Big)}{h}}$ $\times$ $\dfrac{1}{{g{(x+h)}}{g{(x)}}} \Bigg]$
Use product rule of limits for evaluating limit of product of two functions by evaluating product of their limits.
$=\,\,\,$ $\Bigg(\displaystyle \large \lim_{h \,\to\, 0}{\normalsize \dfrac{{g{(x)}}\Big(f{(x+h)}-f{(x)}\Big)-{f{(x)}}\Big(g{(x+h)}-g{(x)}\Big)}{h}} \normalsize \Bigg)$ $\times$ $\Bigg( \displaystyle \large \lim_{h \,\to\, 0}{\normalsize \dfrac{1}{{g{(x+h)}}{g{(x)}}} \Bigg)}$
$=\,\,\,$ $\Bigg(\displaystyle \large \lim_{h \,\to\, 0}{\normalsize \Bigg[\dfrac{{g{(x)}}\Big(f{(x+h)}-f{(x)}\Big)}{h}-\dfrac{{f{(x)}}\Big(g{(x+h)}-g{(x)}\Big)}{h}\Bigg]} \normalsize \Bigg)$ $\times$ $\Bigg( \displaystyle \large \lim_{h \,\to\, 0}{\normalsize \dfrac{1}{{g{(x+h)}}{g{(x)}}} \Bigg)}$
Now, use difference rule of limits for calculating limit of difference of functions by difference of their limits.
$=\,\,\,$ $\Bigg(\displaystyle \large \lim_{h \,\to\, 0}{\normalsize \dfrac{{g{(x)}}\Big(f{(x+h)}-f{(x)}\Big)}{h}}$ $-$ $\displaystyle \large \lim_{h \,\to\, 0}{\normalsize \dfrac{{f{(x)}}\Big(g{(x+h)}-g{(x)}\Big)}{h}} \normalsize \Bigg)$ $\times$ $\Bigg( \displaystyle \large \lim_{h \,\to\, 0}{\normalsize \dfrac{1}{{g{(x+h)}}{g{(x)}}} \Bigg)}$
$=\,\,\,$ $\Bigg(\displaystyle \large \lim_{h \,\to\, 0}{\normalsize \Bigg[g{(x)} \times \dfrac{f{(x+h)}-f{(x)}}{h}\Bigg]}$ $-$ $\displaystyle \large \lim_{h \,\to\, 0}{\normalsize \Bigg[ f{(x)} \times \dfrac{g{(x+h)}-g{(x)}}{h}\Bigg]} \normalsize \Bigg)$ $\times$ $\Bigg( \displaystyle \large \lim_{h \,\to\, 0}{\normalsize \dfrac{1}{{g{(x+h)}}{g{(x)}}} \Bigg)}$
Try product rule of limits and find limit of product of functions in each term of the first factor of the expression.
$=\,\,\,$ $\Bigg(\displaystyle \large \lim_{h \,\to\, 0}{\normalsize g{(x)}}$ $\times$ $\displaystyle \large \lim_{h \,\to\, 0}{\normalsize \dfrac{f{(x+h)}-f{(x)}}{h}}$ $-$ $\displaystyle \large \lim_{h \,\to\, 0}{\normalsize f{(x)}}$ $\times$ $\displaystyle \large \lim_{h \,\to\, 0}{\normalsize \dfrac{g{(x+h)}-g{(x)}}{h}} \normalsize \Bigg)$ $\times$ $\Bigg( \displaystyle \large \lim_{h \,\to\, 0}{\normalsize \dfrac{1}{{g{(x+h)}}{g{(x)}}} \Bigg)}$
$\dfrac{d}{dx}{\, \Bigg(\dfrac{f{(x)}}{g{(x)}}\Bigg)}$ $\,=\,$ $\Bigg(\displaystyle \large \lim_{h \,\to\, 0}{\normalsize g{(x)}}$ $\times$ $\displaystyle \large \lim_{h \,\to\, 0}{\normalsize \dfrac{f{(x+h)}-f{(x)}}{h}}$ $-$ $\displaystyle \large \lim_{h \,\to\, 0}{\normalsize f{(x)}}$ $\times$ $\displaystyle \large \lim_{h \,\to\, 0}{\normalsize \dfrac{g{(x+h)}-g{(x)}}{h}} \normalsize \Bigg)$ $\times$ $\Bigg( \displaystyle \large \lim_{h \,\to\, 0}{\normalsize \dfrac{1}{{g{(x+h)}}{g{(x)}}} \Bigg)}$
Evaluate the limit of first factor of each term in the first factor and second factor by the direct substitution method.
$=\,\,\,$ $\Bigg(g{(x)}$ $\times$ $\displaystyle \large \lim_{h \,\to\, 0}{\normalsize \dfrac{f{(x+h)}-f{(x)}}{h}}$ $-$ $f{(x)}$ $\times$ $\displaystyle \large \lim_{h \,\to\, 0}{\normalsize \dfrac{g{(x+h)}-g{(x)}}{h}} \normalsize \Bigg)$ $\times$ $\Bigg( \dfrac{1}{{g{(x+0)}}{g{(x)}}}\Bigg)$
$=\,\,\,$ $\Bigg(g{(x)}$ $\times$ $\displaystyle \large \lim_{h \,\to\, 0}{\normalsize \dfrac{f{(x+h)}-f{(x)}}{h}}$ $-$ $f{(x)}$ $\times$ $\displaystyle \large \lim_{h \,\to\, 0}{\normalsize \dfrac{g{(x+h)}-g{(x)}}{h}} \normalsize \Bigg)$ $\times$ $\Bigg( \dfrac{1}{{g{(x)}}{g{(x)}}}\Bigg)$
$=\,\,\,$ $\Bigg(g{(x)}$ $\times$ $\displaystyle \large \lim_{h \,\to\, 0}{\normalsize \dfrac{f{(x+h)}-f{(x)}}{h}}$ $-$ $f{(x)}$ $\times$ $\displaystyle \large \lim_{h \,\to\, 0}{\normalsize \dfrac{g{(x+h)}-g{(x)}}{h}} \normalsize \Bigg)$ $\times$ $\Bigg(\dfrac{1}{g{(x)}^2}\Bigg)$
The limit of the function as $h$ approaches $0$ is derivative of the respective function as per the definition of the derivative in limiting operation.
$\implies$ $\dfrac{d}{dx}{\, \Bigg(\dfrac{f{(x)}}{g{(x)}}\Bigg)}$ $\,=\,$ $\Bigg(g{(x)}$ $\times$ $\dfrac{d}{dx}{\, f{(x)}}$ $-$ $f{(x)}$ $\times$ $\dfrac{d}{dx}{\, g{(x)}} \Bigg)$ $\times$ $\Bigg(\dfrac{1}{g{(x)}^2}\Bigg)$
$\implies$ $\dfrac{d}{dx}{\, \Bigg(\dfrac{f{(x)}}{g{(x)}}\Bigg)}$ $\,=\,$ $\dfrac{g{(x)} \times \dfrac{d}{dx}{\, f{(x)}} -f{(x)} \times \dfrac{d}{dx}{\, g{(x)}}}{g{(x)}^2}$
$\,\,\, \therefore \,\,\,\,\,\,$ $\dfrac{d}{dx}{\, \Bigg(\dfrac{f{(x)}}{g{(x)}}\Bigg)}$ $\,=\,$ $\dfrac{g{(x)}\dfrac{d}{dx}{\, f{(x)}} -f{(x)}\dfrac{d}{dx}{\, g{(x)}}}{g{(x)}^2}$
This property is called the quotient rule of derivatives and it is used to find the differentiation of quotient of any two differential functions.
The quotient rule of differentiation is written in two different forms by taking $u = f{(x)}$ and $v = g{(x)}$.
$(1) \,\,\,$ $\dfrac{d}{dx}{\, \Bigg(\dfrac{u}{v}\Bigg)}$ $\,=\,$ $\dfrac{v\dfrac{du}{dx}-u\dfrac{dv}{dx}}{v^2}$
$(2) \,\,\,$ ${d}{\, \Bigg(\dfrac{u}{v}\Bigg)}$ $\,=\,$ $\dfrac{v{du}-u{dv}}{v^2}$
A best free mathematics education website that helps students, teachers and researchers.
Learn each topic of the mathematics easily with understandable proofs and visual animation graphics.
A math help place with list of solved problems with answers and worksheets on every concept for your practice.
Copyright © 2012 - 2022 Math Doubts, All Rights Reserved