JEE Main & Advanced JEE Main Paper Phase-I (Held on 09-1-2020 Morning)

  • question_answer
    The number of real roots of the equation, \[{{e}^{4x}}+{{e}^{3x}}-4{{e}^{2x}}+{{e}^{x}}+1=0\] is           [JEE MAIN Held on 09-01-2020 Morning]

    A) 4           

    B) 2

    C) 3                     

    D) 1

    Correct Answer: D

    Solution :

    [d]  \[\because \,\,\,\,\,\,\,\,\,\,\,({{e}^{4x}}-2{{e}^{2x}}+1)+({{e}^{3x}}-2{{e}^{2x}}+{{e}^{x}})=0\] \[\Rightarrow \,\,\,\,\,\,\,\,\,\,{{({{e}^{2x}}-1)}^{2}}+{{e}^{x}}{{({{e}^{x}}-1)}^{2}}=0\] \[\Rightarrow \,\,\,\,\,\,\,\,\,\,{{({{e}^{x}}-1)}^{2}}\underbrace{[{{({{e}^{x}}+1)}^{2}}+{{e}^{x}}]}_{Always\text{ }positive\text{ }terms}=0\] Hence \[{{e}^{x}}-1=0\] \[\Rightarrow \,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,x=0\] is the only solution


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