JEE Main & Advanced Mathematics Trigonometric Equations Question Bank Critical Thinking

  • question_answer
    In triangle \[ABC\], if \[\angle A=45{}^\circ ,\] \[\angle B=75{}^\circ \], then \[a+c\sqrt{2}\] =   [IIT 1988]

    A) 0

    B) 1

    C) b

    D) 2b

    Correct Answer: D

    Solution :

    \[\angle C={{180}^{o}}-{{45}^{o}}-{{75}^{o}}={{60}^{o}}\] Therefore \[a+c\sqrt{2}=k(\sin A+\sqrt{2}\sin C)\]                                     = \[k\,\left( \frac{1}{\sqrt{2}}+\frac{\sqrt{3}}{2}\sqrt{2} \right)=k\,\left( \frac{1+\sqrt{3}}{\sqrt{2}} \right)\] and \[k=\frac{b}{\sin B}\Rightarrow a+c\sqrt{2}=\frac{b}{\sin {{75}^{o}}}\left( \frac{1+\sqrt{3}}{\sqrt{2}} \right)=2b\].


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