JEE Main & Advanced Mathematics Definite Integration Question Bank Fundamental definite integration, Definite integration by substitution

  • question_answer
    \[\int\limits_{\pi /4}^{3\pi /4}{\frac{dx}{1+\cos x}}\] is equal to                                [IIT 1999]

    A)                 2             

    B)                 \[-2\]

    C)                 \[\frac{1}{2}\]   

    D)                 \[-\frac{1}{2}\]

    Correct Answer: A

    Solution :

               \[\int_{\pi /4}^{3\pi /4}{\frac{dx}{1+\cos x}}\]                    \[\int_{\pi /4}^{3\pi /4}{\frac{1-\cos x}{1-{{\cos }^{2}}x}}\,dx=\int_{\pi /4}^{3\pi /4}{\frac{1-\cos x}{{{\sin }^{2}}x}}\,dx\]                                                     \[=\int_{\pi /4}^{3\pi /4}{(\text{cose}{{\text{c}}^{2}}x}-\cot x\text{cosec}\,x)\,dx\]                                                                \[=\,(-\cot x+\text{cosec}\,x\text{)}_{\pi \text{/4}}^{\text{3}\pi \text{/4}}=2\].


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