SSC Quantitative Aptitude Algebra Question Bank Elementary Algebra (I)

  • question_answer
    If \[x-\sqrt{3}-\sqrt{2}=0\]and \[y-\sqrt{3}+\sqrt{2}=0,\]then the value of \[({{x}^{3}}-20\sqrt{2})-({{y}^{3}}+2\sqrt{2})\]is [SSC CGL Tier II, 2015]

    A) 1

    B) 0

    C) 3

    D) 2

    Correct Answer: B

    Solution :

    [b] \[x-\sqrt{3}-\sqrt{2}=0\]             \[\therefore \]      \[x=\sqrt{3}+\sqrt{x}\]and \[y-\sqrt{3}+\sqrt{2}=0\]             \[\therefore \]      \[y=\sqrt{3}-\sqrt{2}\] Then, \[({{x}^{3}}-20\sqrt{2})-({{y}^{3}}+2\sqrt{2})\] \[={{x}^{3}}-20\sqrt{2}-{{y}^{3}}-2\sqrt{2}\] \[\Rightarrow \]\[{{x}^{3}}-{{y}^{3}}-22\sqrt{2}\]\[\Rightarrow \]\[(x-y)({{x}^{2}}+xy+{{y}^{2}})\]\[-\,22\sqrt{2}\] \[\begin{align}   & =(\sqrt{3}+\sqrt{2}-\sqrt{3}+2)[(\sqrt{3}+{{\sqrt{2)}}^{2}} \\  & \,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,+(\sqrt{3}+\sqrt{2})(\sqrt{3}-2)+{{(\sqrt{3}-\sqrt{2})}^{2}}]-22\sqrt{2} \\ \end{align}\]      \[=2\sqrt{2}(5+2\sqrt{6}+1+5-2\sqrt{6})-22\sqrt{2}\] \[=2\sqrt{2}(11)-22\sqrt{2}=22\sqrt{2}-22\sqrt{2}=0\]


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