The Total solution for NCERT class 6-12
If the points (x, – 1), (2, 1) and (4, 5) are collinear, thenSlope of AB = Slope of BC
Then, (1+1)/(2-x) = (5-1)/(4-2)
2/(2-x) = 4/2
2/(2-x) = 2
2 = 2(2-x)
2 = 4 – 2x
2x = 4 – 2
2x = 2
x = 2/2
= 1
∴ Therequired value of x is 1.