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Coordinate Geometry

by bruin61579 » Mon Apr 25, 2011 7:37 pm
Hi,

I'm trying to reacquaint myself with coordinate geometry. On page 137 of the 12th edition, there's a graph with two points: (-2,4) and (3,-3). How do you determine which pair is (x1, y1) and which pair is (x2, y2), for the slope formula?

Thanks,
David
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by jaymw » Mon Apr 25, 2011 7:56 pm
From your example:

(-2,4) & (3,-3)
(x1,x2) & (y1,y2)

So the slope is: (-3-4)/(3-(-2))= -7/5 = -1.4

The order of the given points does not matter though.

(3,-3) & (-2,4)

Slope: (4-(-3))/(-2-3) = 7/(-5) = -1.4

The only thing you have to remember is that points in the coordinate plane are always given as (x-coordinate,y-coordinate). With that in mind, you can't go wrong.
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by Anurag@Gurome » Mon Apr 25, 2011 8:04 pm
bruin61579 wrote:Hi,

I'm trying to reacquaint myself with coordinate geometry. On page 137 of the 12th edition, there's a graph with two points: (-2,4) and (3,-3). How do you determine which pair is (x1, y1) and which pair is (x2, y2), for the slope formula?

Thanks,
David
It does not matter at all. You can see below:
If (x1, y1) = (-2, 4), and (x2, y2) = (3, -3)
Then slope = (y2 - y1)/(x2 - x1) = (-3 - 4)/(3 + 2) = -7/5

If (x1, y1) = (3, -3), and (x2, y2) = (-2, 4)
Then slope = (y2 - y1)/(x2 - x1) = (4 + 3)/(-2 - 3) = -7/5

So, it can be seen that the slope is the same. I hope that helps.
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