JEE Main & Advanced Mathematics Indefinite Integrals Question Bank Integration by Substitution

  • question_answer
    \[\int_{{}}^{{}}{{{\sec }^{4}}x\tan x\ dx=}\] [AI CBSE 1980, 81; SCRA 1996]

    A)            \[\frac{1}{4}{{\sec }^{4}}x+c\]

    B)            \[4{{\sec }^{4}}x+c\]

    C)            \[\frac{{{\sec }^{3}}x}{3}+c\]

    D)            \[3{{\sec }^{3}}x+c\]

    Correct Answer: A

    Solution :

                       \[\int_{{}}^{{}}{{{\sec }^{4}}tnx\,dx}=\int_{{}}^{{}}{{{\sec }^{3}}x\sec x\tan x\,dx}\]            Put \[t=\sec x\Rightarrow dt=\sec x\tan x\,dx,\] then it reduces to            \[\int_{{}}^{{}}{{{t}^{3}}dt}=\frac{{{t}^{4}}}{4}+c=\frac{1}{4}{{\sec }^{4}}x+c.\]


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