Clear["Global`*"]
reg = ImplicitRegion[ x + k y == 0, {x, y}]
pt = {-((a^2 k)/Sqrt[b^2 + a^2 k^2]), b^2/Sqrt[b^2 + a^2 k^2]}
RegionDistance[reg, pt]
Use codes above all
Why is it impossible to find the distance from this point to the straight line?
The known condition is: a > b > 0, and the point is in the first quadrant. k<0