NCERT Class XI Mathematics - Straight Lines - Solutions

Question : 8

Total: 74

Find the value of x for which the points (x, –1), (2, 1) and (4, 5) are collinear.

Solution:

Let A(x, –1), B(2, 1) and C(4, 5) be the given collinear points. Then by collinearity of A, B, C, we have slope of AB = slope of BC
⇒

1−(−1)

2−x

5−1

4−2

⇒

2−x

= 2
⇒ 2 – x = 1 ⇒ x = 1
Hence for x = 1, A, B & C are collinear.

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