   SEARCH HOME Math Central Quandaries & Queries  Question from Maggie, a student: The question says: Which set of ordered pairs can be used to graph y = -2x-1. A.(-5,9),(1,-3),(4,9) B. (-2,-5),(1,-1),(5,9) C.(-2,-5),(0,-1),(4,-3) D. (-5,9),(-2,3),(4,-9) I cannot figure it out. Could you help me? Maggie,

The problem is saying that one of the three triples of points, A., B., C. or D. are all on the line $y = -2x - 1.$ Your challenge is to determine which triple. Let me try one. I am going to try A.

First point $(-5, 9):$ Substituting $-5 \mbox{ for } x$ gives me $y = (-2 \times -5) -1 = 10 - 1 = 9$ and hence $(-5, 9)$ is on the line.

Second point $(1, -3):$ Substituting $1 \mbox{ for } x$ gives me $y = (1 \times -5) -1 = -6$ and hence $(1, -3)$ is not on the line.

I don't need to check the third point because I am looking for the triple that has all its points on the line.

Now you try B., C. and D.

Penny     Math Central is supported by the University of Regina and The Pacific Institute for the Mathematical Sciences.