CEE Kerala Engineering CEE Kerala Engineering Solved Paper-2011

  • question_answer
    The line parallel to the x-axis and passing through the point of intersection of the lines \[ax+2by+3b=0\]and \[bx-2ay-3a=0,\]where \[(a,b)\ne (0,0)\]is

    A)  above the x-axis at a distance of\[\frac{3}{2}\]

    B)  above the x-axis at a distance of\[\frac{2}{3}\]

    C)  below the x-axis at a distance of\[\frac{2}{3}\]

    D)  below the x-axis at a distance of\[\frac{3}{2}\]

    E)  below the x-axis at a distance of 3

    Correct Answer: D

    Solution :

    Let the line parallel to\[x-\]axis is, \[y=c\]                                                  ...(i) Given lines, \[ax+2by=-3b\]                        ...(ii)          \[bx-2ay=3a\]                         ...(iii) Multiply by b in Eq. (ii) and by a in Eq. (iii), then subtract Eq. (ii) from Eq. (iii), \[\begin{align}   & \underline{\begin{align}   & abx+2{{b}^{2}}y=-3{{b}^{2}} \\  & xab-2{{a}^{2}}y=3{{a}^{2}} \\  & -\,\,\,\,\,\,\,\,+\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,- \\ \end{align}} \\  & 2({{a}^{2}}+{{b}^{2}})y=-3({{a}^{2}}+{{b}^{2}}) \\ \end{align}\] \[\Rightarrow \]                               \[y=-\frac{3}{2}\] From Eq. (i),       \[c=-\frac{3}{2}\] Hence, the line is, \[y=-\frac{3}{2}\] Which is passing through the point of intersection of the lines Eqs. (ii) and (iii) below the\[x-\]axis at a distance of\[\frac{3}{2}\].


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