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

  • question_answer
    \[\int_{{}}^{{}}{\frac{\sqrt{\tan x}}{\sin x\cos x}}\ dx=\] [Bihar CEE 1974; MP PET 2002; Kerala (Engg.) 2002]

    A)            \[2\sqrt{\sec x}+c\]

    B)            \[2\sqrt{\tan x}+c\]

    C)            \[\frac{2}{\sqrt{\tan x}}+c\]

    D)            \[\frac{2}{\sqrt{\sec x}}+c\]

    Correct Answer: B

    Solution :

                       \[\int_{{}}^{{}}{\frac{\sqrt{\tan x}}{\sin x\cos x}\,dx}=\int_{{}}^{{}}{\frac{\tan x}{\sqrt{\tan x}\sin x\cos x}dx}\]                    \[=\int_{{}}^{{}}{\frac{\sin x\sec x}{\sqrt{\tan x}\sin x\cos x}\,dx}=\int_{{}}^{{}}{\frac{{{\sec }^{2}}x}{\sqrt{\tan x}}\,dx}\]            Put \[t=\tan x\Rightarrow dt={{\sec }^{2}}x\,dx,\] then it reduces to            \[\int_{{}}^{{}}{\frac{1}{\sqrt{t}}\,dt}=2{{t}^{1/2}}+c=2\sqrt{\tan x}+c\].


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