RAJASTHAN ­ PET Rajasthan PET Solved Paper-2006

  • question_answer
    For\[{{x}^{12}}-{{x}^{9}}+{{x}^{4}}-x+1>0,\]the greatest interval is

    A)  \[0<x<1\]        

    B)  \[-4<x\le 0\]

    C)  \[0<x<\infty \]         

    D)  \[-10<x<10\]

    Correct Answer: C

    Solution :

     Given, \[{{x}^{12}}-{{x}^{9}}+{{x}^{4}}-x+1>0\] If \[x\le 0,\]then \[{{x}^{12}}-{{x}^{9}}+{{x}^{4}}-x+1>0\] If \[0<x<1,\]then \[{{x}^{12}}-{{x}^{9}}+{{x}^{4}}-x+1\] \[={{x}^{12}}+{{x}^{4}}(1-{{x}^{5}})-x+1>0\] If \[x\ge 1,\]then \[{{x}^{12}}-{{x}^{9}}+{{x}^{4}}-x+1>0\] Hence, the greatest interval is\[0<x<\infty \].


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