math
posted by barb .
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?
x1x2/y1y2
Can you please help me through this?

The slope of a line through two given points P1(x1,y1) and P2(x2,y2) is given by the expression:
m=(y2y1)/(x2x1)
Since y2=y1, so y2y1=0.
Next we have to check if the slope exists:
(x2x1)=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.