Question 28

Mathematics Line Hard

The lines \(px+qy=1\) and \(qx+py=1\) are respectively the sides AB, AC of the triangle ABC and the base BC is bisected at \((p,q)\). Equation of the median of the triangle through the vertex A is

(A) \((2pq-1)(qx+py-1)-(p^2+q^2-1)(px+qy-1)=0\)
(B) \((2pq-1)(px+qy-1)+(p^2+q^2-1)(qx+py-1)=0\)
(C) \((2pq-1)(px+qy-1)-(p^2+q^2-1)(qx+py-1)=0\)
(D) \((2pq-1)(qx+py-1)+(p^2+q^2-1)(px+qy-1)=0\)
✓ Correct Answer: Option C Verified Solution

📘 Step-by-Step Solution & Detailed Explanation:

The median will pass through \(A\) and the midpoint of the opposite side, i.e., \((p, q)\). The general equation of the line that passes through the intersection point of the lines \(AC\) and \(AB\) is: \[ (px + qy - 1) + \lambda (qx + py - 1) = 0 \] As this line passes through the point \((p, q)\), hence: \[ (p^2 + q^2 - 1) + \lambda (2pq - 1) = 0 \Rightarrow \lambda = - \frac{p^2 + q^2 - 1}{(2pq - 1)} \] Putting this value of \(\lambda\), we get the desired equation: \[ (px + qy - 1) - \left( \frac{p^2 + q^2 - 1}{2pq - 1} \right)(qx + py - 1) = 0 \] Or \[ (2pq - 1)(px + qy - 1) - (p^2 + q^2 - 1)(qx + py - 1) = 0 \]

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