JEE Main & Advanced Mathematics Straight Line Question Bank Distance between two lines, Perpendicular distance of the line from a point Position of point w.r.t. line

  • question_answer
    The distance between the lines \[3x+4y=9\]and \[6x+8y=15\]is   [MNR 1982; RPET 1995; MP PET 2002]

    A)            3/2 

    B)            3/10

    C)            6    

    D)            None of these

    Correct Answer: B

    Solution :

               Here the lines are, \[3x+4y-9=0\]            ......(i)                    and                      \[6x+8y-15=0\]     ......(ii)                    Now distance from origin of both the lines are                    \[\frac{-9}{\sqrt{{{3}^{2}}+{{4}^{2}}}}=-\frac{9}{5}\]and \[\frac{-15}{\sqrt{{{6}^{2}}+{{8}^{2}}}}=-\frac{15}{10}\]                    Hence distance between both the lines are \[\,\left| \,-\frac{9}{5}-\left( -\frac{15}{10} \right)\, \right|\,=\frac{3}{10}\].                    Ailter: Put \[y=0\] in the first equation, we get \[x=3\]therefore, the point (3, 0) lies on it. So the required distance between these two lines is the perpendicular length of the line \[6x+8y=15\] from the point (3, 0).  i.e., \[\frac{6\times 3-15}{\sqrt{{{6}^{2}}+{{8}^{2}}}}=\frac{3}{10}\].


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