SSC Sample Paper Mock Test-2 SSC CGL Tear-II Paper-1

  • question_answer
    If \[x=\frac{\sqrt{m+3n}+\sqrt{m-3n}}{\sqrt{m+3n}-\sqrt{m-3n}},\]then

    A)  \[3n{{x}^{2}}-2mx+3n=0\]

    B)  \[2n{{x}^{2}}-2mx+3n=0\]

    C)  \[3n{{x}^{2}}-2mx-3n=0\]

    D)  \[3n{{x}^{2}}+3mx+3n=0\]

    Correct Answer: A

    Solution :

    \[\frac{x}{1}=\frac{\sqrt{m+3n}+\sqrt{m-3n}}{\sqrt{m+3n}-\sqrt{m-3n}}\]
    By componendo and dividendo rule,
    \[\frac{x+1}{x-1}=\frac{\sqrt{m+3n}+\sqrt{m-3n}+\sqrt{m+3n}-\sqrt{m-3n}}{\sqrt{m+3n}+\sqrt{m-3n}-\sqrt{m+3n}+\sqrt{m-3n}}\]
    \[\Rightarrow \]\[\frac{x+1}{x-1}=\frac{\sqrt{m+3n}}{\sqrt{m-3n}}\]
    Squaring both sides,
    \[\frac{{{(x+1)}^{2}}}{{{(x-1)}^{2}}}=\frac{m+3n}{m-3n}\]
    Applying componendo and dividendo rule,
    \[\frac{{{(x+1)}^{2}}+{{(x-1)}^{2}}}{{{(x+1)}^{2}}-{{(x-1)}^{2}}}=\frac{m+3n+m-3n}{m+3n-m+3n}\]
    \[\Rightarrow \]\[\frac{2\,\,({{x}^{2}}+1)}{2\,\,(2x)}=\frac{2m}{2\,\,(3n)}\]
    \[\Rightarrow \]\[\frac{{{x}^{2}}+1}{2x}=\frac{m}{3n}\]
    \[\Rightarrow \]\[3n{{x}^{2}}-2mx+3n=0\]


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