Which of the following points is collinear with (0,0) and (2,1)?

A) (-2,-1)

B) (-1,-2)

C) (-1,2)

D) (1,-2)

E) (1,2)

It’s pretty quick just to draw these all and see, but it’s even *faster* to recognize that when a line goes through (0, 0), then all of its other points will tell you the slope all by themselves. This is because slope, generally speaking, is change in *y* divided by change in *x*, calculated thusly:

When one of the points is (0, 0), that simplifies:

So really here all you’re looking for is another set of points with the same ratio as (2, 1) has. (–2, –1) works perfectly.