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

  • question_answer
    In \[\Delta ABC,\]\[{{a}^{2}}+{{b}^{2}}+{{c}^{2}}=ac+ab\sqrt{3},\]then triangle is  [MP PET 2004]

    A) Equilateral

    B) Isosceles

    C) Right angled

    D) None of these

    Correct Answer: C

    Solution :

    We have, \[{{a}^{2}}+{{b}^{2}}+{{c}^{2}}-ac-ab\sqrt{3}=0\] \[\frac{{{a}^{2}}}{4}-\,ac+{{c}^{2}}+\frac{3{{a}^{2}}}{4}+{{b}^{2}}-ab\sqrt{3}=0\] \[{{\left[ \frac{a}{2}-c \right]}^{2}}+{{\left[ \frac{\sqrt{3}a}{2}-b \right]}^{2}}=0\] i.e, \[a=2c\] and \[2b=\sqrt{3}a\] i.e., \[{{b}^{2}}+{{c}^{2}}={{a}^{2}}\] Hence triangle is right angled.


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