If $\mathrm{f}(x)=x^2+1$ and $\mathrm{g}(x)=\frac{1}{x}$, then the value of…

If $\mathrm{f}(x)=x^2+1$ and $\mathrm{g}(x)=\frac{1}{x}$, then the value of $\mathrm{f}(\mathrm{g}(\mathrm{g}(\mathrm{f}(x))))$ at $x=1$ is
  1. $4$
  2. $1$
  3. $5$
  4. $3$

Solution

$\begin{aligned} \mathrm{f}(x)=x^2+1, & \mathrm{~g}(x)=\frac{1}{x} \\ \therefore \quad \mathrm{f}(\mathrm{g}(\mathrm{g}(\mathrm{f}(x)))) & =\mathrm{f}\left(\mathrm{g}\left(\mathrm{g}\left(x^2+1\right)\right)\right) \\ & =\mathrm{f}\left(\mathrm{g}\left(\frac{1}{x^2+1}\right)\right) \\ & =\mathrm{f}\left(x^2+1\right) \\ & =\left(x^2+1\right)^2+1 \end{aligned}$ $\therefore \quad$ At $x=1$, we get the value of above function $\begin{aligned} & =\left[(1)^2+1\right]^2+1 \\ & =5 \end{aligned}$

Asked in: MHT CET 2023 (12 May Shift 2)

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