Manipal Engineering Manipal Engineering Solved Paper-2012

  • question_answer
    If\[\alpha +\beta +\gamma =\pi \],   then   the   value   of\[{{\sin }^{2}}\alpha +{{\sin }^{2}}\beta -{{\sin }^{2}}\gamma \]is equal to

    A) \[2\sin \alpha \]                               

    B) \[2\sin \alpha cos\beta sin\gamma \]

    C) \[2\sin \alpha \sin \beta \cos \gamma \]

    D) \[2\sin \alpha \sin \beta \sin \gamma \]

    Correct Answer: C

    Solution :

    \[\therefore \]\[{{\sin }^{2}}\alpha +\sin (\beta -\gamma )\sin (\beta +\gamma )\] \[={{\sin }^{2}}\alpha +\sin (\pi -\alpha )\sin (\beta -\gamma )\] \[=\sin \alpha [\sin \alpha +\sin (\beta -\gamma )]\] \[=\sin \alpha [\sin (\pi -(\beta +\gamma ))+\sin (\beta -\gamma )]\] \[=\sin \alpha [\sin (\beta -\gamma )+\sin (\beta +\gamma )]\] \[=2\sin \alpha \sin \beta \cos \gamma \]


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