Q.If \(x = 9 + 4\sqrt{5}\), then the value of \(\sqrt{x} - \frac{1}{\sqrt{x}}\) will be — (a) 4 (b) 3 (c) 2 (d) 1
Answer: A
Let \(x = 9 + 4\sqrt{5}\)   = \(5 + 4 + 4\sqrt{5}\)   = \((\sqrt{5})^2 + (2)^2 + 2 \cdot \sqrt{5} \cdot 2\)   = \((\sqrt{5} + 2)^2\) ∴ \(\sqrt{x} = \sqrt{5} + 2\) ∴ \(\frac{1}{\sqrt{x}} = \frac{1}{\sqrt{5} + 2}\)   = \(\frac{\sqrt{5} - 2}{(\sqrt{5} + 2)(\sqrt{5} - 2)}\)   = \(\frac{\sqrt{5} - 2}{5 - 4}\)   = \(\sqrt{5} - 2\) ∴ \(\sqrt{x} - \frac{1}{\sqrt{x}} = (\sqrt{5} + 2) - (\sqrt{5} - 2)\)   = \(\sqrt{5} + 2 - \sqrt{5} + 2 = 4\)
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