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

  • question_answer
    If, x, y and z are perpendiculars drawn on a, b and c, respectively, then the value of \[\frac{bx}{c}+\frac{cy}{a}+\frac{az}{b}\] will be

    A) \[\frac{{{a}^{2}}+{{b}^{2}}+{{c}^{2}}}{2R}\]

    B) \[\frac{{{a}^{2}}+{{b}^{2}}+{{c}^{2}}}{R}\]

    C) \[\frac{{{a}^{2}}+{{b}^{2}}+{{c}^{2}}}{4R}\]

    D) \[\frac{2({{a}^{2}}+{{b}^{2}}+{{c}^{2}})}{R}\]

    Correct Answer: A

    Solution :

    [a] Let area of triangle be \[\Delta \], then according to question,
    \[\Delta =\frac{1}{2}ax=\frac{1}{2}by=\frac{1}{2}cz\therefore \frac{bx}{c}+\frac{cy}{a}+\frac{az}{b}\]
    \[=\frac{b}{c}\left( \frac{2\Delta }{a} \right)+\frac{c}{a}\left( \frac{2\Delta }{b} \right)+\frac{a}{b}\left( \frac{2\Delta }{c} \right)\]
    \[=\,\,\frac{2\Delta ({{b}^{2}}+{{c}^{2}}+{{a}^{2}})}{abc}\]
    \[=\frac{2({{a}^{2}}+{{b}^{2}}+{{c}^{2}})}{abc}.\frac{abc}{4R}=\frac{{{a}^{2}}+{{b}^{2}}+{{c}^{2}}}{2R}\]


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