Straight Line and Pair of Straight Lines 1 Question 21

21. If $P S$ is the median of the triangle with vertices $P(2,2)$, $Q(6,-1)$ and $R(7,3)$, then equation of the line passing through $(1,-1)$ and parallel to $P S$ is

(2014 Main, 2000)

(a) $4 x-7 y-11=0$

(b) $2 x+9 y+7=0$

(c) $4 x+7 y+3=0$

(d) $2 x-9 y-11=0$

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Solution:

  1. Coordinate of $S=\frac{7+6}{2}, \frac{3-1}{2}=\frac{13}{2}, 1$

$[\because S$ is mid-point of line $Q R]$

Slope of the line $P S$ is $\frac{-2}{9}$.

Required equation passes through $(1,-1)$ and parallel to $P S$ is

$$ \begin{aligned} y+1 & =\frac{-2}{9}(x-1) \\ \Rightarrow \quad 2 x+9 y+7 & =0 \end{aligned} $$



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