(10) y = 1 log ϵ x {\displaystyle y={\dfrac {1}{\log _{\epsilon }x}}} .
d y d x = log ϵ x × 0 − 1 × 1 x log ϵ 2 x = − 1 x log ϵ 2 x . {\displaystyle {\frac {dy}{dx}}={\frac {\log _{\epsilon }x\times 0-1\times {\dfrac {1}{x}}}{\log _{\epsilon }^{2}x}}=-{\frac {1}{x\log _{\epsilon }^{2}x}}.}
(11) y = log ϵ x 3 = ( log ϵ x ) 1 3 {\displaystyle y={\sqrt[{3}]{\log _{\epsilon }x}}=(\log _{\epsilon }x)^{\frac {1}{3}}} . Let y = z 1 3 {\displaystyle y=z^{\frac {1}{3}}} .
d y d z = 1 3 z − 2 3 ; d z d x = 1 x ; d y d x = 1 3 x log ϵ 2 x 3 . {\displaystyle {\frac {dy}{dz}}={\frac {1}{3}}z^{-{\frac {2}{3}}};\quad {\frac {dz}{dx}}={\frac {1}{x}};\quad {\frac {dy}{dx}}={\frac {1}{3x{\sqrt[{3}]{\log _{\epsilon }^{2}x}}}}.}
(12) y = ( 1 a x ) a x {\displaystyle y=\left({\dfrac {1}{a^{x}}}\right)^{ax}} .
log ϵ y = a x ( log ϵ 1 − log ϵ a x ) = − a x log ϵ a x . 1 y d y d x = − a x × a x log ϵ a − a log ϵ a x . a n d d y d x = − ( 1 a x ) a x ( x × a x + 1 log ϵ a + a log ϵ a x ) . {\displaystyle {\begin{aligned}\log _{\epsilon }y&=ax(\log _{\epsilon }1-\log _{\epsilon }a^{x})=-ax\log _{\epsilon }a^{x}.\\{\frac {1}{y}}\,{\frac {dy}{dx}}&=-ax\times a^{x}\log _{\epsilon }a-a\log _{\epsilon }a^{x}.\\and\quad \quad \quad {\frac {dy}{dx}}&=-\left({\frac {1}{a^{x}}}\right)^{ax}(x\times a^{x+1}\log _{\epsilon }a+a\log _{\epsilon }a^{x}).\end{aligned}}}
Try now the following exercises.
Exercises XII. (See page 260 for Answers.)
(1) Differentiate y = b ( ϵ a x − ϵ − a x ) {\displaystyle y=b(\epsilon ^{ax}-\epsilon ^{-ax})} .
(2) Find the differential coefficient with respect to t {\displaystyle t} of the expression u = a t 2 + 2 log ϵ t {\displaystyle u=at^{2}+2\log _{\epsilon }t} .
(3) if y = n t {\displaystyle y=n^{t}} , find d ( log ϵ y ) d t {\displaystyle {\dfrac {d(\log _{\epsilon }y)}{dt}}} .
(4) Show that if y = 1 b ⋅ a b x log ϵ a {\displaystyle y={\dfrac {1}{b}}\cdot {\dfrac {a^{bx}}{\log _{\epsilon }a}}} ; d y d x = a b x {\displaystyle {\dfrac {dy}{dx}}=a^{bx}} .
(5) If w = p v n {\displaystyle w=pv^{n}} , find d w d v {\displaystyle {\dfrac {dw}{dv}}} .