JEE Main & Advanced JEE Main Paper (Held On 9 April 2016)

  • question_answer
    If m and M are the minimum and the maximum values of \[4+\frac{1}{2}{{\sin }^{2}}2x-2{{\cos }^{4}}x,x\in R,\]then M-m is equal to   JEE Main Online Paper (Held On 09 April 2016)

    A) \[\frac{7}{4}\]                   

    B) \[\frac{15}{4}\]                

    C) \[\frac{9}{4}\]   

    D) \[\frac{1}{4}\]

    Correct Answer: C

    Solution :

                    \[4+\frac{1}{2}{{\sin }^{2}}2x-\frac{1}{2}{{(2{{\cos }^{2}}x)}^{2}}\] \[=4+\frac{1}{2}{{\sin }^{2}}2x-\frac{1}{2}{{(1+\cos 2x)}^{2}}=-{{\cos }^{2}}2x-\cos 2x+4=-\]        \[[{{\cos }^{2}}2x+\cos 2x-4]=\frac{17}{4}-{{\left( \cos 2x+\frac{1}{2} \right)}^{2}}\] M = maximum value \[=\frac{17}{4}\] m = minimum value = 2 \[M-m=\frac{17}{4}-2=\frac{9}{4}.\]                


You need to login to perform this action.
You will be redirected in 3 sec spinner