Q.If \(\sqrt{x} + \sqrt{y} = \sqrt{18 + 6\sqrt{5}}\), what is the value of \(x\)? (a) 8 (b) 15 (c) 6 (d) 12
Answer: B
\(\sqrt{x} + \sqrt{y} = \sqrt{18 + 6\sqrt{5}}\) Or, \(\sqrt{x} + \sqrt{y} = \sqrt{18 + 2\sqrt{45}}\) Or, \(\sqrt{x} + \sqrt{y} = \sqrt{(\sqrt{15})^2 + (\sqrt{3})^2 + 2 \cdot \sqrt{15} \cdot \sqrt{3}}\) Or, \(\sqrt{x} + \sqrt{y} = \sqrt{(\sqrt{15} + \sqrt{3})^2}\) Or, \(\sqrt{x} + \sqrt{y} = \sqrt{15} + \sqrt{3}\) \(\therefore x = 15\)
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