Posted by **barb** on Sunday, August 22, 2010 at 9:21pm.

find the slope of the line, if it exists:

coordinates are (-1,-5), (1,-5)

I am doing something wrong because I either get 5 or if I work it another way I get 0

m= either 5 or 0

Which one is it if any?

x1-x2/y1-y2

Can you please help me through this?

- math -
**MathMate**, Sunday, August 22, 2010 at 9:34pm
The slope of a line through two given points P1(x1,y1) and P2(x2,y2) is given by the expression:

m=(y2-y1)/(x2-x1)

Since y2=y1, so y2-y1=0.

Next we have to check if the slope exists:

(x2-x1)=1-(-1)=2 ≠ 0.

Therefore m=0/2=0.

Note: if y2=y1 and x2=x1, then P1 and P2 are two coincident points, and the slope does not exist, because we cannot define a line through two coincident points.

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