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SSC Sample Paper Mock Test-13 SSC CGL Tear-II Paper-1

  • question_answer
    If \[x+y=7,\] then what is the value of\[{{x}^{3}}+{{y}^{3}}+21xy?\]

    A) 243      

    B)  343

    C)  441     

    D)  729

    Correct Answer: B

    Solution :

    By question, \[x+y=7\] Then, \[{{x}^{3}}+{{y}^{3}}+21xy\] \[={{(x+y)}^{3}}-3xy\,\,(x+y)+21xy\] \[={{(7)}^{3}}-3xy\,\,(7)+21xy\] \[=343-21xy+21xy=343\]


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