If the points A(1, 2), O(0, 0) and C(a, b) are collinear then
(a) a = b (b) a = 2b (c) 2a = b (d) a+b = 0
Given points are (1,2), (0,0) and (a,b).
These points are collinear if their slopes are equal.
Now, slope of AB =y2−y1x2−x1=0−20−1=2
and slope of BC= b−0a−0=ba
So, ba=2
⇒b=2a
So, the correct choice is (c).