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JEE Main & Advanced Mathematics Trigonometric Equations Question Bank Relation between sides and angles, Solutions of triangles

  • question_answer
    In \[\Delta ABC\], \[c\cos (A-\alpha )+a\cos (C+\alpha )=\]

    A) \[a\cos \alpha \]

    B) \[b\cos \alpha \]

    C) \[c\cos \alpha \]

    D) \[2b\cos \alpha \]

    Correct Answer: B

    Solution :

    \[c\cos (A-\alpha )+a\cos (C+\alpha )\]\[=c(\cos A\cos \alpha +\sin A\sin \alpha )\]\[+a(\cos C\cos \alpha -\sin C\sin \alpha )\] \[=\cos \alpha (c\cos A+a\cos C)+c\,\sin A\sin \alpha -a\sin C\sin \alpha \] Þ \[b\cos \alpha +kac\sin \alpha -kac\sin \alpha =b\cos \alpha \].


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