Quotient Rule of Differentiation

Example 1:

$$ y=\frac{(2x^3+5)}{(x-7)},\;\;\; \textup{Find} \;\;\frac{dy}{dx}$$

Solution:

$$ y=\frac{(2x^3+5)}{(x-7)}$$ $$ \frac{dy}{dx}=\frac{d}{dx} \frac{(2x^3+5)}{(x-7)}$$ $$ \because\;\; \frac{d}{dx} \frac{u}{v}= \frac{v \frac{du}{dx}-u \frac{dv}{dx}}{v^2}$$ $$ \therefore\;\; \frac{dy}{dx}=\frac{(x-7)\frac{d}{dx}(2x^3+5)-(2x^3+5)\frac{d}{dx}(x-7)}{(x-7)^2}$$ $$ \frac{dy}{dx}=\frac{(x-7)(\frac{d}{dx}2x^3+\frac{d}{dx}5)-(2x^3+5)(\frac{d}{dx}x-\frac{d}{dx}7)}{(x-7)^2}$$ $$ \frac{dy}{dx}=\frac{(x-7)(2\frac{d}{dx}x^3+\frac{d}{dx}5)-(2x^3+5)(\frac{d}{dx}x-\frac{d}{dx}7)}{(x-7)^2}$$ $$ \because\;\; \frac{d}{dx} x^n=nx^{n-1} ,\;\;\; \frac{d}{dx} x=1 \;\;\; \textup{and} \;\;\; \frac{d}{dx} c=0$$ $$ \frac{dy}{dx}=\frac{(x-7)(2(3x^{3-1})+0)-(2x^3+5)(1-0)}{(x-7)^2}$$ $$ \frac{dy}{dx}=\frac{(x-7)(2(3x^2))-(2x^3+5)(1)}{(x-7)^2}$$ $$ \frac{dy}{dx}=\frac{(x-7)(6x^2)-(2x^3+5)}{(x-7)^2}$$ $$ \frac{dy}{dx}=\frac{6x^3-42x^2-2x^3-5}{(x-7)^2}$$ $$ \frac{dy}{dx}=\frac{4x^3-42x^2-5}{(x-7)^2}$$