JEE Main & Advanced Mathematics Straight Line Question Bank Slope of line, Equation of line in different forms

  • question_answer
    The equation of the lines on which the perpendiculars from the origin make \[{{30}^{o}}\]angle with x?axis and which form a triangle of area \[\frac{50}{\sqrt{3}}\] with axes, are

    A)            \[x+\sqrt{3}y\pm 10=0\]      

    B)            \[\sqrt{3}x+y\pm 10=0\]

    C)            \[x\pm \sqrt{3}y-10=0\]        

    D)            None of these

    Correct Answer: B

    Solution :

               Let p be the length of the perpendicular from the origin on the given line. Then its equation in normal form is \[x\cos {{30}^{o}}+y\sin {{30}^{o}}=p\]or \[\sqrt{3}x+y=2p\]                    This meets the coordinate axes at \[A\left( \frac{2p}{\sqrt{3}},0 \right)\] and \[B(0,\,2p)\].  \ Area of \[\Delta OAB=\frac{1}{2}\left( \frac{2p}{\sqrt{3}} \right)\text{ }2p=\frac{2{{p}^{2}}}{\sqrt{3}}\]                    By hypothesis \[\frac{2{{p}^{2}}}{\sqrt{3}}=\frac{50}{\sqrt{3}}\Rightarrow p=\pm 5\].                    Hence the lines are \[\sqrt{3}x+y\pm 10=0\].


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