If $f(x)=\frac{a^x-a^{-x}}{a^x+a^{-x}}$, where a, $x$ satisfy the necessary conditions, then $f^{-1}(x)=$
If $f(x)=\frac{a^x-a^{-x}}{a^x+a^{-x}}$, where a, $x$ satisfy the necessary conditions, then $f^{-1}(x)=$
- $\frac{1}{2} \log _a\left(\frac{1+x}{1-x}\right)$
- $\frac{1}{2} \log _a\left(\frac{1+x}{x}\right)$
- $\frac{1}{2} \log _a\left(\frac{2+x}{2-x}\right)$
- $\frac{1}{2} \log _a\left(\frac{x}{1-x}\right)$
Solution
$\begin{aligned} & y=\frac{a^x-a^{-x}}{a^x+a^{-x}}=\frac{a^{2 x}-1}{a^{2 x}+1} \\ & \Rightarrow y\left(a^{2 x}+1\right)=a^{2 x}-1 \\ & \Rightarrow a^{2 x}=\frac{1+y}{1-y} \\ & \Rightarrow x=\frac{1}{2} \log _a\left(\frac{1+y}{1-y}\right) \\ & \Rightarrow f^{-1}(x)=\frac{1}{2} \log _a\left(\frac{1+x}{1-x}\right)\end{aligned}$
Asked in: MHT CET 2022 (07 Aug Shift 1)
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