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8th Class Mathematics Algebraic Expressions Question Bank Algebraic Expressions & Identities

  • question_answer
    If \[\left( \mathbf{a}+\mathbf{b}+\mathbf{c} \right)=\mathbf{15}\] and \[(ab+bc+ca)=74,\] find the value of \[\left( {{a}^{2}}+{{b}^{2}}+{{c}^{2}} \right)\]

    A)  67                               

    B)  77              

    C)  57                               

    D)  37

    Correct Answer: B

    Solution :

    (b): Focus on what is to be found \[{{a}^{2}}+{{b}^{2}}+{{c}^{2}}={{\left( a+b+c \right)}^{2}}-2\left( ab+bc+ca \right)\]\[={{\left( 15 \right)}^{2}}-2\times 74\] \[=225-148=77.\]


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