JEE Main & Advanced Mathematics Straight Line Question Bank Angle between two straight lines, Bisector of angle between two lines

  • question_answer
    Angle between the lines \[\frac{x}{a}+\frac{y}{b}=1\] and \[\frac{x}{a}-\frac{y}{b}=1\] is  [MP PET 1995]

    A)            \[2{{\tan }^{-1}}\frac{b}{a}\]    

    B)            \[{{\tan }^{-1}}\frac{2ab}{{{a}^{2}}+{{b}^{2}}}\]

    C)            \[{{\tan }^{-1}}\frac{{{a}^{2}}-{{b}^{2}}}{{{a}^{2}}+{{b}^{2}}}\]              

    D) None of these

    Correct Answer: A

    Solution :

    The lines are \[bx+ay-ab=0\]and\[bx-ay-ab=0\]. Hence the required angle is                    \[{{\tan }^{-1}}\left| \frac{ab-(-ab)}{{{b}^{2}}+(-{{a}^{2}})} \right|={{\tan }^{-1}}\left| \frac{2ab}{{{b}^{2}}-{{a}^{2}}} \right|=2{{\tan }^{-1}}\frac{b}{a}\].


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