find slope must shpw work
when given two points on a line, the easiest way to calculate the slope is take the difference of the y in point 1 minus y in point 2 and divide that by the differences of the x's
m - slope
p_{1} - (-6,-9) ⇒ x_{1} = -6 and y_{1} = -9
p_{2} - (-6,6) ⇒ x_{2} = -6 and y_{2} = 6
m = (y_{1}-y_{2})/(x_{1}-x_{2})
Substituting in the values for x_{1}, x_{2}, y_{1}, y_{2}
you get
m = ((-9)-6)/((-6)-(-6)) = -15/(-6+6) = -15/0 ⇒ undefined
hmm but we can't divide by zero, which is of course why this slope value is "undefined"
This is a unique line that is vertical or parallel to the y-axis