JEE Main & Advanced Mathematics Conic Sections Question Bank Mock Test - Conic Sections

  • question_answer
    If a line \[y=3x+1\]cuts the parabola \[{{x}^{2}}-4x-4y+20=0\]at A and B, then the tangent of the angle subtended by line segment AB, at the origin is

    A) \[8\sqrt{3}/205\]        

    B) \[8\sqrt{3}/209\]

    C) \[8\sqrt{3}/215\]        

    D) None of these

    Correct Answer: B

    Solution :

    [b] The joint equation of OA and OB is \[{{x}^{2}}-4x(y-3x)-4y(y-3x)+20{{(y-3x)}^{2}}=0\] Making the equation of the parabola homogeneous using straight line. We get \[{{x}^{2}}(1+12+180)-{{y}^{2}}(4-20)-xy(4-12+120)=0\]or \[193{{x}^{2}}+16{{y}^{2}}-112xy=0\] \[\tan \theta =\frac{2\sqrt{{{h}^{2}}-ab}}{a+b}\] \[=\frac{2\sqrt{{{56}^{2}}-193\times 16}}{193+16}=\frac{8\sqrt{3}}{209}\]


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