Manipal Engineering Manipal Engineering Solved Paper-2012

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

    A) \[1\,\,sq\,\,unit\]                           

    B) \[2\,\,sq\,\,units\]

    C) \[\frac{\sqrt{3}}{2}sq\,\,units\]

    D)        \[\sqrt{3}\,\,sq\,\,units\]

    Correct Answer: D

    Solution :

    We have,\[\frac{\cos A}{a}=\frac{\cos B}{b}=\frac{\cos C}{c}\] \[\Rightarrow \]               \[\frac{\cos A}{k\sin A}=\frac{\cos B}{k\sin B}=\frac{\cos C}{k\sin C}\] \[\Rightarrow \]               \[\cot A=\cot B=\cot C\] \[\Rightarrow \]               \[A=B=C={{60}^{o}}\] \[\therefore \,\,\Delta \,\,ABC\]is an equilateral triangle. \[\therefore \]Area of triangle\[=\frac{\sqrt{3}}{4}{{a}^{2}}\]                 \[=\frac{\sqrt{3}}{4}\times {{2}^{2}}=\sqrt{3}\,\,sq\,\,units\]


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