8th Class Mathematics Factorisation Question Bank Factorisation

  • question_answer
    Which of the following is the factor of \[12{{({{a}^{2}}+7a)}^{2}}-8({{a}^{2}}+7a)(2a-1)-15{{(2a-1)}^{2}}\]?
    (i) \[(2{{a}^{2}}+8a+3)\]           
    (ii) \[(6{{a}^{2}}+52a-5)\]
    (iii) \[\text{(3a+5)}\]              

    A)  Only (i)                      

    B)  Both (i) and (ii)          

    C)  Only (ii)                     

    D)  All (i), (ii) and (iii)      

    Correct Answer: B

    Solution :

    We have, \[12{{({{a}^{2}}+7a)}^{2}}-8({{a}^{2}}+7a)(2a-1)-15{{(2a-1)}^{2}}\] \[=12{{({{a}^{2}}+7a)}^{2}}-18({{a}^{2}}+7a)(2a-1)\]             \[+10({{a}^{2}}+7a)(2a-1)-15{{(2a-1)}^{2}}\] \[=6({{a}^{2}}+7a)[2({{a}^{2}}+7a)-3(2a-1)]\]             \[+5(2a-1)[2{{a}^{2}}+7a)-3(2a-1)]\] \[=(6{{a}^{2}}+42a)(2{{a}^{2}}+8a+3)\]             \[+(10a-5)(2{{a}^{2}}+8a+3)\] \[=(6{{a}^{2}}+42a+10a-5)(2{{a}^{2}}+8a+3)\] \[=(6{{a}^{2}}+52a-5)(2{{a}^{2}}+8a+3)\]


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