JEE Main & Advanced Mathematics Trigonometric Equations Question Bank Solution of trigonometrical equations

  • question_answer
    If \[1+\cot \theta =\text{cosec}\theta \], then the general value of \[\theta \] is  [Roorkee 1981]

    A) \[n\pi +\frac{\pi }{2}\]

    B) \[2n\pi -\frac{\pi }{2}\]

    C) \[2n\pi +\frac{\pi }{2}\]

    D) None of these

    Correct Answer: C

    Solution :

    \[\frac{1}{\sin \theta }=1+\frac{\cos \theta }{\sin \theta }\Rightarrow \sin \theta +\cos \theta =1\] \[\Rightarrow \] \[\cos \left( \theta -\frac{\pi }{4} \right)\,=\cos \frac{\pi }{4}\Rightarrow \theta -\frac{\pi }{4}=2n\pi \pm \frac{\pi }{4}\] Hence\[\theta =2n\pi \] or\[\theta =2n\pi +\frac{\pi }{2}\]. But \[\theta =2n\pi \] is ruled out.


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