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SSC Sample Paper SSC CGL - Sample Paper-8

  • question_answer
    If \[{{a}^{2}}+{{b}^{2}}+{{c}^{2}}=20\] and \[a+b+c=0,\] then \[ab+bc+ac=?\]

    A)  10                               

    B)  \[-\,10\]

    C)  20                               

    D)  \[-\,20\]

    Correct Answer: B

    Solution :

    \[{{(a+b+c)}^{2}}={{a}^{2}}+{{b}^{2}}+{{c}^{2}}+2\,(ab+bc+ca)\] \[\Rightarrow \]   \[0=20+2(ab+bc+ca)\] \[\Rightarrow \]   \[ab+bc+ca=\frac{-\,20}{2}=-10\]


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