JEE Main & Advanced Mathematics Straight Line Question Bank Mock Test - Straight Lines

  • question_answer
    If the quadrilateral formed by the lines \[ax+by+c=0,\text{ }a'x+b'y+c'=0,\text{ }ax+by+c'=0,\text{ }a'x+b'y+c'=0\]has perpendicular diagonals, then

    A)  \[{{b}^{2}}+{{c}^{2}}=b{{'}^{2}}+c{{'}^{2}}\]

    B)  \[{{c}^{2}}+{{a}^{2}}=c{{'}^{2}}+a{{'}^{2}}\]

    C)  \[{{a}^{2}}+{{b}^{2}}=a{{'}^{2}}+b{{'}^{2}}\]

    D)  none of these

    Correct Answer: C

    Solution :

    [c] Since the diagonals are perpendicular, the given quadrilateral is a rhombus. So the distances between two pairs of parallel sides are equal, hence, \[\left| \frac{c'-c}{\sqrt{{{a}^{2}}+{{b}^{2}}}} \right|=\left| \frac{c'-c}{\sqrt{a{{'}^{2}}+b{{'}^{2}}}} \right|\] Or \[{{a}^{2}}+{{b}^{2}}=a{{'}^{2}}+b{{'}^{2}}\]


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