Slope of line intersecting with y axis

Hi,

I am trying to caluclate the slope of a line intersecting with one of the axes. I do understand that, as shown in the figure below, the slopw in case (a) is the where θ is the angle between the line and the x axis. But what about case (b)? What is the slope when the line intersects with the y axis and the angle θ becomes between the line and the y axis. is the slope becomes the ?

% case a
slope_a = tan(theta) % or y2-y1/x2-x1

%case b
slope_b = cot(theta) % or x2-x1/y2-y1 

Thanks.

Answer 1

[John D'Errico]

What has this to do with MATLAB?

The axis has NOTHING to do with the slope!!!!

The slope in both cases is (y2 - y1)/(x2 - x1). Which axis a line intersects is completely irrelevant. In fact, do you see the line ALWAYS intersects both axes, unless the line is exactly horizontal or vertical. In the case of a vertical line of course, the slope is undefined.

How you define the ANGLE a line intersects with an axis is irrelevant, as slope is not represented by an angle. Yes, you can compute that angle, but then surely you would recognize that the angle a line makes when it intersects with the two axes is always given by the angles of a right triangle, and therefore one angle is 90 degrees minus the other?