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8th Class Mathematics Cubes and Cube Roots Question Bank Cubes and Cube Roots

  • question_answer
    The cube of a number \[x\] is nine times of\[x\], then find\[x\], where \[x\ne 0\] and \[x\ne -3\].

    A)  8                                

    B)         2        

    C)         4                                

    D)         3        

    Correct Answer: D

    Solution :

    It is given that,\[{{x}^{3}}=9x,x\ne 0,x\ne -3\] Now, \[{{x}^{3}}-9x=0\Rightarrow x({{x}^{2}}-9)=0\] \[\Rightarrow {{x}^{2}}-9=0(\because x\ne 0)\] \[\Rightarrow {{x}^{2}}=9\Rightarrow x=3\] or \[-3\] But \[x\ne -3\therefore x=3\]


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