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

  • question_answer
    The base BC of a triangle ABC is bisected at the point (p, q) and the equations to the sides AB and AC are respectively \[x+y+3=0\] and \[qx+py=1.\] Then the equation to the median through A is

    A)            \[2x-y=9\]

    B)            \[({{p}^{2}}+{{q}^{2}}-1)(px+qy-1)=(2p-1)(qx+py-1)\]

    C)            \[(pq-1)(px+qy-1)=({{p}^{2}}+{{q}^{2}}-1)(qx+py-1)\]

    D)            None of these                          

    Correct Answer: A

    Solution :

               Since the median passes through A, the intersection of the given lines. Its equation is given by \[(px+qy-1)+\lambda (qx+py-1)=0\], where \[\lambda \] is some real number. Also, since the median passes through the point (p, q), we have \[({{p}^{2}}+{{q}^{2}}-1)+\lambda (qp+pq-1)=0\]                    Þ \[\lambda =-\frac{{{p}^{2}}+{{q}^{2}}-1}{2pq-1}\] and the equation of median through A is \[(px+qy-1)-\frac{{{p}^{2}}+{{q}^{2}}-1}{2pq-1}(qx+py-1)=0\]                    Þ \[(2pq-1)(px+qy-1)=({{p}^{2}}+{{q}^{2}}-1)(qx+py-1)\].


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