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7th Class Mathematics Algebraic Expressions Question Bank Algebraic Expressions

  • question_answer
    The value of \[9{{x}^{2}}+49{{y}^{2}}-42xy\] when \[x=15\]and \[y=3\]is ____.

    A)  636                            

    B)  576                

    C)  456                            

    D)  386

    Correct Answer: B

    Solution :

    When \[x=15\] and \[y=3,\] we have \[9\times {{(15)}^{2}}+49\times {{(3)}^{2}}-42\times 15\times 3\] \[=2025+441-1890=576\]


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