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

  • question_answer
    The parallelism condition for two straight lines one of which is specified by the equation \[ax+by+c=0\]the other being represented parametrically by \[x=\alpha \text{ }t+\beta ,\] \[y=\gamma \text{ }t+\delta \]  is given by                                                              [AMU 2000]

    A)            \[\alpha \gamma -b\alpha =0\], \[\beta =\delta =c=0\]           

    B)            \[a\alpha -b\gamma =0\], \[\beta =\delta =0\]

    C)            \[a\alpha +b\gamma =0\]       

    D)            \[a\gamma =b\alpha =0\]

    Correct Answer: C

    Solution :

               Given lines are \[ax+by+c=0\]                                 .....(i)                    and \[x=\alpha \,t+\beta ,\,y=\gamma \,t+\delta \]                             After eliminating t, we get \[\gamma \,x-\alpha \,y+\alpha \delta -\gamma \,\beta =0\]                                                                                                 .....(ii)                    For parallelism condition, \[\frac{a}{\gamma }=\frac{b}{-\alpha }\]Þ \[a\alpha +b\gamma =0\].


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