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

  • question_answer
    In a \[\Delta ABC\] if the sides are \[a=3,\,b=5\] and \[c=4\], then \[\sin \frac{B}{2}+\cos \frac{B}{2}\] is equal to [Karnataka CET 2005]

    A) \[\sqrt{2}\]

    B) \[\frac{\sqrt{3}+1}{2}\]

    C) \[\frac{\sqrt{3}-1}{2}\]

    D) 1

    Correct Answer: A

    Solution :

    \[a=3,b=5,c=4,\,\,s=\frac{a+b+c}{2}=\frac{12}{2}=6\] \[\sin \frac{B}{2}=\sqrt{\frac{(s-c)(s-a)}{ca}}=\sqrt{\frac{2.3}{12}}=\sqrt{\frac{1}{2}}\] \[\cos \frac{B}{2}=\sqrt{\frac{s(s-b)}{ca}}=\sqrt{\frac{6.1}{12}}=\sqrt{\frac{1}{2}}\] \\[\sin \frac{B}{2}+\cos \frac{B}{2}=\frac{2}{\sqrt{2}}=\sqrt{2}\].


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