NCERT Class XI Mathematics - Straight Lines - Solutions

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Question : 21
Total: 74
Passing through the points (–1, 1) and (2, –4).
Solution:  
Let the given points be A(–1, 1) and B(2, –4).
We know that the equation of a line passing through the given points
(x1,y1) and (x2,y2) is given by
yy1
xx1
=
y2y1
x2x1

Here, x1 = – 1, y1 = 1, x2 = 2, y2 = – 4
So, the equation of a line passing through the given points is
y1
x(1)
=
(41)
2(1)
y1
x+1
=
5
3
⇒ 3 (y - 1) = - 5 (x + 1) ⇒ 5x + 3y + 2 = 0
Hence, the required equation is 5x + 3y + 2 = 0.
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