Math CentralQuandaries & Queries


Question from Maggie, a student:

The question says:

Which set of ordered pairs can be used to graph y = -2x-1.

B. (-2,-5),(1,-1),(5,9)
D. (-5,9),(-2,3),(4,-9)

I cannot figure it out. Could you help me?


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.


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