J & K CET Engineering J and K - CET Engineering Solved Paper-2013

  • question_answer
    The equation of a straight line upon which the length of the perpendicular from the origin is 5 and slope of this perpendicular is \[3/4\] is

    A)  \[2x+5y\pm 16=0\]

    B)  \[4x+3y\pm 25=0\]

    C)  \[4x+3y\pm 5=0\]

    D)  \[2x+5y\pm 4=0\]

    Correct Answer: B

    Solution :

    Let \[y=mx+c\]be the equation of straight line \[\Rightarrow \] \[mx-y+c=0\] ??(i) Now, by condition Perpendicular distance from origin to line (i) = 5 \[\Rightarrow \] \[\frac{|0-0+c|}{\sqrt{{{m}^{2}}+1}}=5\] \[\Rightarrow \] \[c=\pm 5\sqrt{{{m}^{2}}\pm 1}\] ?..(ii) Also, given that Slope of perpendicular to line (i) from the origin \[=\frac{3}{4}\] \[\Rightarrow \] \[-\frac{1}{m}=\frac{3}{4}\] \[\Rightarrow \] \[m=\frac{-4}{3}\] From Eq. (ii), \[c=\pm 5\sqrt{{{m}^{2}}+1}\]\[c=\pm 5\sqrt{1+\frac{16}{9}}=\pm 5\times \frac{5}{3}=\pm \frac{25}{3}\] On putting the values of m and c in Eq. (i), we get \[-\frac{4x}{3}-y\pm \frac{25}{3}=0\] \[\Rightarrow \] \[4x+3y\pm 25=0\] which is required equation of straight line.


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