BCECE Engineering BCECE Engineering Solved Paper-2001

  • question_answer
    If \[\sin \theta +\cos \theta =1,\] then the general value of \[\theta \] is:

    A) \[2n\pi \]                                            

    B)  \[n\pi +{{(-1)}^{n}}\frac{\pi }{4}-\frac{\pi }{4}\]

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

    D)         none of these

    Correct Answer: B

    Solution :

    Since, \[\sin \theta +\cos \theta =1\] \[\Rightarrow \]\[\sqrt{2}\left( \frac{1}{\sqrt{2}}\sin \theta +\frac{1}{\sqrt{2}}\cos \theta  \right)=1\] \[\Rightarrow \]               \[\sqrt{2}\sin \left( \frac{\pi }{4}+\theta  \right)=1\] \[\Rightarrow \]               \[\sin \left( \frac{\pi }{4}+\theta  \right)=\frac{1}{\sqrt{2}}=\sin \left( \frac{\pi }{4} \right)\] \[\therefore \] The general value is                                 \[\frac{\pi }{4}+\theta =n\pi +{{(-1)}^{n}}\frac{\pi }{4}\]                 \[\Rightarrow \]               \[\theta =n\pi +{{(-1)}^{n}}\frac{\pi }{4}-\frac{\pi }{4}\]


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