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Railways Sample Paper RRBs Assistant Loco Pilot and Technician CBT STAGE-I Sample Paper-6

  • question_answer
    If the sum and difference of two expressions are \[5{{a}^{2}}-a-4\] and \[{{a}^{2}}+9a-10\] respectively, then their LCM is

    A)  \[(a-1)(a+1)(3a-7)\]

    B)  \[(a-1)(3a-7)(2a-3)\]

    C)  \[(a-1)(3a+7)(2a-3)\]

    D)  \[(a-1)(3a-7)(2a+3)\]

    Correct Answer: C

    Solution :

    Let expression are X and Y, then \[X+Y\,=5{{a}^{2}}-a-4\] \[X-Y={{a}^{2}}+9a-10\] \[\therefore \,\,\,\]            \[X=\frac{1}{2}(6{{a}^{2}}+8a-14)\] \[=3{{a}^{2}}+4a-7\] \[=(a-1)(3a+7)\] and \[Y=\frac{1}{2}(4{{a}^{2}}-10a+6)\] \[=2{{a}^{2}}-5a+3=(a-1)(2a-3)\] \[\therefore \] LCM of X and Y \[=(a-1)(3a+7)(2a-3)\]


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