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

  • question_answer
    Evaluate the expression \[81\text{ }{{p}^{2}}+16{{q}^{2}}-72pq\]when \[p=\frac{2}{3}\]. and \[q=\frac{3}{4}\] .

    A)  \[-16\]                                

    B)  \[9\]                    

    C)         \[-9\]                   

    D)         \[16\]

    Correct Answer: B

    Solution :

    Given \[p=\frac{2}{3}\] and \[q=\frac{3}{4}\] \[81{{p}^{2}}+16{{q}^{2}}-72pq\] \[=81{{\left( \frac{2}{3} \right)}^{2}}+16{{\left( \frac{3}{4} \right)}^{2}}-72\left( \frac{2}{3} \right)\left( \frac{3}{4} \right)\] \[=81\times \frac{4}{9}+16\times \frac{9}{16}-\frac{72}{2}\] \[=36+9-36=9\]


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