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SSC Sample Paper Mock Test-20 SSC CGL Tear-II Paper-1

  • question_answer
    If \[a+b+c=13,{{a}^{2}}+{{b}^{2}}+{{c}^{2}}=69,\]then \[(ab+bc+ca)\] is equal to

    A) 60

    B)  50

    C)  75

    D)  80

    Correct Answer: B

    Solution :

    We have \[{{(a+b+c)}^{2}}=({{a}^{2}}+{{b}^{2}}+{{c}^{2}})+2\,\,(ab+bc+ca)\] \[\Rightarrow \]   \[{{(13)}^{2}}=69+2\,\,(ab+bc+ca)\] \[\Rightarrow \]   \[2\,\,(ab+bc+ca)=(169-69)=100\] \[\Rightarrow \]   \[(ab+bc+ca)=50\]


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