JEE Main & Advanced JEE Main Paper (Held On 11-Jan-2019 Morning)

  • question_answer
    In a triangle, the sum of lengths of two sides is x and the product of the lengths of the same two sides is y. If \[{{x}^{2}}-{{c}^{2}}=y,\]where c is the length of the third side of the triangle, then the circum radius of the triangle is [JEE Main Online Paper (Held On 11-Jan-2019 Morning]

    A) \[\frac{y}{\sqrt{3}}\]                                         

    B)               \[\frac{c}{3}\]

    C)               \[\frac{c}{\sqrt{3}}\]                                         

    D)               \[\frac{3}{2}y\]

    Correct Answer: C

    Solution :

    Let a and b be the two sides of the triangle. Then, \[a+b=x\] and \[ab=y\] Now,\[{{x}^{2}}-{{c}^{2}}=y\Rightarrow {{(a+b)}^{2}}-{{c}^{2}}=ab\] \[\Rightarrow \]\[{{a}^{2}}+{{b}^{2}}-{{c}^{2}}=-ab\] \[\Rightarrow \]\[\frac{{{a}^{2}}+{{b}^{2}}-{{c}^{2}}}{2ab}=-\frac{1}{2}\] \[\Rightarrow \]\[\cos C=-\frac{1}{2}\] \[\Rightarrow \]\[\angle C=\frac{2\pi }{3}\] Now, let R be the circumradius of the triangle. \[\therefore \]\[R=\frac{c}{2\sin C}=\frac{c}{\sqrt{3}}\]


You need to login to perform this action.
You will be redirected in 3 sec spinner