CEE Kerala Engineering CEE Kerala Engineering Solved Paper-2007

  • question_answer
    The acute angle between the lines joining the origin to the points of intersection of the line\[\sqrt{3}x+y=2\]and the  circle  is\[{{x}^{2}}+{{y}^{2}}=4,\]is

    A)  \[\pi /2\]            

    B)         \[\pi /3\]

    C)  \[\pi /4\]            

    D)         \[\pi /6\]

    E)  \[\pi /12\]

    Correct Answer: B

    Solution :

    Equation of line is \[\sqrt{3}x+y=2\]                                         ...(i) and equation of circle is \[{{x}^{2}}+{{y}^{2}}=4\]                                           ...(ii) From Eqs. (i) and (ii), we get \[{{x}^{2}}+2{{(-\sqrt{3}x)}^{2}}=4\] \[\Rightarrow \]               \[{{x}^{2}}+4+3{{x}^{2}}-4\sqrt{3}x=4\] \[\Rightarrow \]               \[4{{x}^{2}}-4\sqrt{3}x=0\] \[\Rightarrow \]               \[x(x-\sqrt{3})=0\] \[\Rightarrow \]               \[x=0,\sqrt{3}\] \[\therefore \]Points of intersection of line and circle are (0,2) and\[(\sqrt{3},-1)\]. Slope of line joining (0, 0) and (0, 2) \[=\frac{2-0}{0-0}=\infty \Rightarrow {{\theta }_{1}}=\frac{\pi }{2}\] And slope of line joining (0, 0) and\[(\sqrt{3},-1)\] \[=\frac{-1}{\sqrt{3}}\Rightarrow {{\theta }_{2}}=\frac{\pi }{6}\]. Required angle\[=\frac{\pi }{2}-\frac{\pi }{6}=\frac{\pi }{3}\]


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