JEE Main & Advanced Mathematics Complex Numbers and Quadratic Equations Question Bank De Moivre's theorem and Roots of unity

  • question_answer
    \[{{(\sin \theta +i\,\cos \theta )}^{n}}\,\]is equal to [RPET 2001]

    A) \[\cos n\theta +i\,\sin n\theta \]

    B) \[\sin n\theta +i\,\cos n\theta \]

    C) \[\cos n\left( \frac{\pi }{2}-\theta  \right)+i\,\sin n\left( \frac{\pi }{2}-\theta  \right)\]

    D) None of these

    Correct Answer: C

    Solution :

    \[{{(\sin \theta +i\cos \theta )}^{n}}\]\[={{\left[ \cos \left( \frac{\pi }{2}-\theta  \right)+i\sin \left( \frac{\pi }{2}-\theta  \right) \right]}^{n}}\] = \[\cos n\left( \frac{\pi }{2}-\theta  \right)+i\sin n\left( \frac{\pi }{2}-\theta  \right)\].


You need to login to perform this action.
You will be redirected in 3 sec spinner