 Hello friends, let's discuss the following question. It says, find the value of x for which the points x-1, 2, 1 and 4, 5 are collinear. Let us now understand the criteria for three points to be collinear. Three points say a, b, c are collinear slope of a, b is equal to slope of b, c. So this knowledge will work as the idea. Let us now proceed on with the solution. The given three points are x-1, b, 2, 1 and c, 4, 5. Now the points a, b and c are collinear if slope of a, b is equal to slope of b, c. Now the slope of a, b is given by y2 minus y1 that is 1 minus minus 1 upon x2 minus x1 that is 2 minus x. And slope of b, c is given by 5 minus 1 upon 4 minus 2 and this implies 2 upon 2 minus x is equal to 4 upon 2. And this again implies 2 upon 2 minus x is equal to 2 and this implies 2 minus x is equal to 1 and this implies x is equal to 1. Hence the answer is x is equal to 1. So for x is equal to 1 the points a, b and c will be collinear. So this completes the question. Hope you enjoyed this session. Goodbye and take care.