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

  • question_answer
    If the equation \[y=mx+c\] and \[x\cos \alpha +y\sin \alpha =p\] represents the same straight line, then

    A)            \[p=c\sqrt{1+{{m}^{2}}}\]       

    B)            \[c=p\sqrt{1+{{m}^{2}}}\]       

    C)            \[cp=\sqrt{1+{{m}^{2}}}\]       

    D)                 \[{{p}^{2}}+{{c}^{2}}+{{m}^{2}}=1\]

    Correct Answer: B

    Solution :

               If the given lines represent the same line, then the length of the perpendiculars from the origin to the lines are equal, so that \[\frac{c}{\sqrt{1+{{m}^{2}}}}=\]\[\frac{p}{\sqrt{{{\cos }^{2}}\alpha +{{\sin }^{2}}\alpha }}\]                    \[\Rightarrow \] \[c=p\sqrt{1+{{m}^{2}}}\].


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