JEE Main & Advanced Mathematics Triangles & Properties of Triangle Question Bank Self Evaluation Test - Properties of Triangles and Height & Dstances

  • question_answer
    In a \[\Delta ABC\], if \[\frac{\cos A}{a}=\frac{\cos B}{b}=\frac{\cos C}{c},\] and the side \[a=2,\] then area of the triangle is

    A) 1

    B) 2

    C) \[\frac{\sqrt{3}}{2}\]

    D) \[\sqrt{3}\]

    Correct Answer: D

    Solution :

    [d] \[\frac{\cos A}{a}=\frac{\cos B}{b}=\frac{\cos C}{c}\] \[\Rightarrow \frac{\cos A}{2R\sin A}=\frac{\cos B}{2R\sin B}=\frac{\cos C}{2R\sin C}\] \[\Rightarrow \cot A=\cot B=\cot C\] \[\Rightarrow A=B=C=60{}^\circ \Rightarrow \Delta ABC\] is equilateral Hence, \[\Delta =\frac{\sqrt{3}}{4}{{a}^{2}}=\sqrt{3}.\]


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