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

  • question_answer
    A line L is perpendicular to the line \[5x-y=1\]and the area of the triangle formed by the line L and coordinate axes is 5. The equation of the line L is                                                            [IIT 1980; RPET 1997]

    A)            \[x+5y=5\]                              

    B)            \[x+5y=\pm 5\sqrt{2}\]

    C)            \[x-5y=5\]                                

    D)             \[x-5y=5\sqrt{2}\]

    Correct Answer: B

    Solution :

               A line perpendicular to the line \[5x-y=1\]is given by\[x+5y-\lambda =0=L\], (given)                    In intercept form \[\frac{x}{\lambda }+\frac{y}{\lambda /5}=1\]                    So, area of triangle is \[\frac{1}{2}\]\[\times \](Multiplication of intercepts)                    Þ \[\frac{1}{2}(\lambda )\times \left( \frac{\lambda }{5} \right)=5\Rightarrow \lambda =\pm 5\sqrt{2}\]                    Hence the equation of required straight line is\[x+5y=\pm 5\sqrt{2}\] .


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