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

  • question_answer
    Add : \[5{{x}^{2}}-\frac{1}{3}x+\frac{5}{2},-\frac{1}{2}{{x}^{2}}+\frac{1}{2}x-\frac{1}{3}\] and \[-2{{x}^{2}}+\frac{1}{5}x-\frac{1}{6}\].

    A)  \[\frac{5}{2}{{x}^{2}}+\frac{11}{30}x+2\]      

    B)  \[\frac{3}{2}{{x}^{2}}+\frac{30}{11}x+3\]      

    C)  \[\frac{5}{2}{{x}^{2}}+\frac{13}{30}x+1\]      

    D)  \[\frac{3}{4}{{x}^{2}}+\frac{12}{11}x+5\]

    Correct Answer: A

    Solution :

    Required sum \[=\left( 5{{x}^{2}}-\frac{1}{3}x+\frac{5}{2} \right)+\left( -\frac{1}{2}{{x}^{2}}+\frac{1}{2}x-\frac{1}{3} \right)\]                                     \[+\left( -2{{x}^{2}}+\frac{1}{5}x-\frac{1}{6} \right)\] \[=5{{x}^{2}}-\frac{1}{2}{{x}^{2}}-2{{x}^{2}}-\frac{1}{3}x+\frac{1}{2}x+\frac{1}{5}x\]                                     \[+\frac{5}{2}-\frac{1}{3}-\frac{1}{6}\]                         [Collecting like terms] \[=\left( 5-\frac{1}{2}-2 \right){{x}^{2}}+\left( -\frac{1}{3}+\frac{1}{2}+\frac{1}{5} \right)x\]                                     \[+\left( \frac{5}{2}-\frac{1}{3}-\frac{1}{6} \right)\] \[=\left( \frac{10-1-4}{2} \right){{x}^{2}}+\left( \frac{-10+15+6}{30} \right)x\] \[+\left( \frac{15-2-1}{6} \right)\] \[=\frac{5}{2}{{x}^{2}}+\frac{11}{30}x+2\]


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