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

  • question_answer
    \[\int_{{}}^{{}}{\frac{\sin 2x}{{{a}^{2}}+{{b}^{2}}{{\sin }^{2}}x}}\ dx=\] [Roorkee 1977]

    A)            \[\frac{1}{{{b}^{2}}}\log ({{a}^{2}}+{{b}^{2}}{{\sin }^{2}}x)+c\] 

    B)            \[\frac{1}{b}\log ({{a}^{2}}+{{b}^{2}}{{\sin }^{2}}x)+c\]

    C)            \[\log ({{a}^{2}}+{{b}^{2}}{{\sin }^{2}}x)+c\]                               

    D)            \[{{b}^{2}}\log ({{a}^{2}}+{{b}^{2}}{{\sin }^{2}}x)+c\]

    Correct Answer: A

    Solution :

                       Put \[{{a}^{2}}+{{b}^{2}}{{\sin }^{2}}x=t\Rightarrow {{b}^{2}}\sin 2x\,dx=dt,\] then                    \[\int_{{}}^{{}}{\frac{\sin 2x}{{{a}^{2}}+{{b}^{2}}{{\sin }^{2}}x}\,dx=\frac{1}{{{b}^{2}}}\int_{{}}^{{}}{\frac{dt}{t}=\frac{1}{{{b}^{2}}}\log t+c}}\]                                                                    \[=\frac{1}{{{b}^{2}}}\log ({{a}^{2}}+{{b}^{2}}{{\sin }^{2}}x)+c.\]


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