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NCERT Class XI Mathematics - Straight Lines - Solutions

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Question : 21 of 74
Marks: +1, -0
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)(x_1, y_1) and (x2,y2)(x_2, y_2) is given by
y−y1x−x1\frac{y-y_1}{x-x_1} = y2−y1x2−x1\frac{y_2-y_1}{x_2-x_1}
Here, x1x_1 = – 1, y1y_1 = 1, x2x_2 = 2, y2y_2 = – 4
So, the equation of a line passing through the given points is
y−1x−(−1)\frac{y-1}{x-(-1)} = −4−12−(−1)\frac{-4-1}{2-(-1)} ⇒ y−1x+1\frac{y-1}{x+1} = −53\frac{-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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