Question 1203348
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Looking at the x coordinates of the three points, we see B is between A and C.  So the three points are collinear if the slope from A to B is the same as the slope from B to C.<br>
Informally, you can see the slopes are the same by seeing that the change in the x value from A to B is 3 times the change in the x value from B to C while the change in y from A to B is also 3 times the change in the y value from B to C.<br>
Using the given coordinates, the x value changes by 3 from A to B and changes by 1 from B to C; the change in x from A to B is 3 times the change in x from B to C.<br>
The three points are collinear if the change in y from A to B is 3 times the change in y from B to C.  From A to B the change in y is -150 and from B to C the change in y is -50; -150 is 3 times -50, so the points are collinear.<br>
This is an informal method that shows the points are collinear by seeing that the slope from A to B and the slope from B to C are the same -- but without using the formal formula for determining the slopes.<br>