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5. Continuity and Differentiation
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If the function $f(x) = - 4{e^{\left( {\frac{{1 - x}}{2}} \right)}} + 1 + x + \frac{{{x^2}}}{2} + \frac{{{x^3}}}{3}$ and $g(x)=f^{-1}(x) \,;$ then the value of $g'(-\frac{7}{6})$ equals
A
$\frac{1}{5}$
B
$- \frac{1}{5}$
C
$\frac{6}{7}$
D
$ -\frac{6}{7}$
Solution
$\because g(x)=f^{1}(x)$
${g f(x)=x}$
${g^{1} f(x) f^{\prime}(x)=1}$
$(\because f(1)=-7 / 6)$
$\therefore \mathrm{g}^{1}(\mathrm{f}(1))=\frac{1}{\mathrm{f}^{2}(1)}$
$g^{1}(-7 / 6)=\frac{1}{5}$
Standard 12
Mathematics