Too much Fortran for me:-)

I think r + ve means radius with a positive value. (ve meaning value???)
On second thought, I think that r + ve, means use the positive version of radius. (ve meaning version)

Looking at the ax + by +c = 0 equation,

a = (-/+ radiusL +/- radiusK) * (xL - xK) - ...

where xL means the x coordinate of the center point L of circle L.
rL means the radius of circle L.

The inner and outer tangent line equations are calculated using the 4 combinations of +/- radiusL and +/- radiusK
So the math is not as abstruse as I initially thought.

How to convert ax + by + c = 0 into a MoI line segment???

- Brian

AI conclusions may or may not be faulty, but:

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To plot a line from the equation "ax + by + c = 0," you need to first rearrange the equation to solve for y (to get it in slope-intercept form, "y = mx + b"), then find the y-intercept (b) and the slope (m), and use those values to plot the line on a graph by finding two points on the line and connecting them; you can also find the x and y intercepts directly by plugging in 0 for y and x respectively and solving for the other variable.