Question
If f is a real function satisfying $\text{f}\Big(\text{x}+\frac{1}{\text{x}}\Big)=\text{x}^2+\frac{1}{\text{x}^2}$ for all $\text{x}\in\text{R}-\{0\},$ then write the expression for f(x).

Answer

We have,$\text{f}\Big(\text{x}+\frac{\text{1}}{{\text{x}}}\Big) = \text{x}^2+\frac{1}{\text{x}}$
Now,
$\text{x}^2+\frac{1}{\text{x}^2} = \Big(\text{x}+\frac{1}{\text{x}}\Big)^2-2$ $\big[\because(\text{a}+\text{b})^2=\text{a}^2+\text{b}^2+2\text{ab}\big]$
$\Rightarrow\text{f}\Big(\text{x}+\frac{1}{\text{x}}\Big)=\Big(\text{x}+\frac{1}{\text{x}}\Big)^2-2$
$\Rightarrow\text{f}(\text{x})=\text{x}^2-2,\text{where } |\text{x}|\geq2$

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