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

  • question_answer
    Simplify: \[\frac{3}{2}{{x}^{2}}({{x}^{2}}-1)+\frac{1}{4}{{x}^{2}}({{x}^{2}}+x)-\frac{3}{4}x({{x}^{3}}-1)\]

    A)  \[{{x}^{4}}+\frac{1}{2}{{x}^{3}}+\frac{1}{4}{{x}^{2}}+x\]

    B)  \[2{{x}^{4}}+\frac{1}{4}{{x}^{3}}-\frac{3}{4}{{x}^{2}}+\frac{1}{4}x\]

    C)  \[{{x}^{4}}+\frac{1}{4}{{x}^{3}}-\frac{3}{2}{{x}^{2}}+\frac{3}{4}x\]

    D)  \[2{{x}^{4}}+\frac{3}{4}{{x}^{3}}-\frac{1}{4}{{x}^{2}}+\frac{3}{4}x\]

    Correct Answer: C

    Solution :

    We have, \[\frac{3}{2}{{x}^{2}}({{x}^{2}}-1)+\frac{1}{4}{{x}^{2}}({{x}^{2}}+x)-\frac{3}{4}x({{x}^{3}}-1)\] \[=\frac{3}{2}{{x}^{4}}-\frac{3}{2}{{x}^{2}}+\frac{1}{4}{{x}^{4}}+\frac{1}{4}{{x}^{3}}-\frac{3}{4}{{x}^{4}}+\frac{3}{4}x\] \[=\frac{3}{2}{{x}^{4}}+\frac{1}{4}{{x}^{4}}-\frac{1}{4}{{x}^{4}}+\frac{1}{4}{{x}^{3}}-\frac{3}{4}{{x}^{2}}+\frac{3}{4}x\] \[=\frac{6{{x}^{4}}+{{x}^{4}}-3{{x}^{4}}}{4}+\frac{1}{4}{{x}^{3}}-\frac{3}{2}{{x}^{2}}+\frac{3}{4}x\] \[={{x}^{4}}+\frac{1}{4}{{x}^{3}}-\frac{3}{2}{{x}^{2}}+\frac{3}{4}x\]


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