Verified answer

Slope m = (y2 - y1) / (x2 - x1) = (9 + 3) / (2 - 2) = 12/0 = undefined

Also m = tanA

So TanA will be undefined at A = 90 degree

Slope is nothing but angle made by the line joining those two points with x-axis which is nothing but 90 degree

The slope of the line connecting two points is the difference in the Y values divided by the difference in the X values. It doesn't matter which point goes first as long as you do it the same direction for both X and Y

In this case lets go from A to P Difference in Y = -3 -9 = -12 Difference in X = 2 - 2 = 0 -12/0 Since you can't divide by zero the line connecting these two points do not have a slope which means it must be a vertical line. Which it is because the values of X are both 2 so the line connecting A and P is a vertical line at X=2 and it doesn't matter what the value of Y is, the value of X will always be 2.

If two points happen to have the same value for X then they will represent a horizontal line and that slope will always be zero because the difference in the Y's will always be zero and anything divided into zero will always be zero.

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

m=(9-(-3))/(2-2) no slope.

It is a vertical line x=2