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

  • question_answer
    Find the value of a if\[pqa={{(~3p+q)}^{2}}-{{(3p-q)}^{2}}\].

    A)  11                              

    B)  21                  

    C)  10                  

    D)         12

    Correct Answer: D

    Solution :

    We have, \[pqa={{(3p+q)}^{2}}-{{(3p-q)}^{2}}\] \[=(3p+q+3p-q)(3p+q-3p+q)\]             \[\text{ }\!\![\!\!\text{ Using }{{x}^{2}}-{{y}^{2}}=(x+y)(x-y)]\] \[=6p\times 2q\] \[\Rightarrow pqa=12pq\] \[\therefore a=\frac{12pq}{pq}=12\]


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