12th Class Mathematics Applications of Derivatives Question Bank Case Based (MCQs) - Derivatives

  • question_answer
    If \[f\left( x \right)={{e}^{x}}\,\sin \,x\], then \[f'''\left( x \right)=\]

    A) \[2{{e}^{x}}\left( \sin \,x+\cos \,x \right)\]

    B) \[2{{e}^{x}}\left( \cos x-\sin x \right)\]

    C) \[2{{e}^{x}}\left( \sin \,x-\cos \,x \right)\]

    D) \[2{{e}^{x}}\,\cos x\]

    Correct Answer: B

    Solution :

    we have, \[f\left( x \right)={{e}^{x}}\sin x\] \[\Rightarrow \,f'\left( x \right)={{e}^{x}}\cos \,x+{{e}^{x}}\sin \,x={{e}^{x}}\left( \cos \,x+\sin x \right)\] \[\left( x \right)={{e}^{x}}\left( \cos x-\sin x \right)+{{e}^{x}}\left( \cos x+\sin x \right)\] \[=2{{e}^{x}}\cos x\] \[\Rightarrow f'''\left( x \right)=2\left[ {{e}^{x}}\cos x-{{e}^{x}}\sin x \right]=2{{e}^{x}}\left[ \cos x-\sin \,x \right]\]


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