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

  • question_answer
    If the sides of a triangle are \[3,\ 5,\ 7,\]then [MP PET 1996]

    A) All its angles are acute

    B) One angle is obtuse

    C) Triangle is right angled

    D) None of these

    Correct Answer: B

    Solution :

    \[\cos C=\frac{{{3}^{2}}+{{5}^{2}}-{{7}^{2}}}{2\times 3\times 5}\Rightarrow C=120{}^\circ \].


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