Oh yeah. I had a shoulder line with a slope. Needed to make a dart perpendicular to shoulder line at the midpoint. Aha! Get slope of shoulder line, negate & invert to get perpendicular slope. Use midpoint as center point of circle. Solve line and circle equations simultaneously. My issues were that python doesn’t like ^ for exponents, likes ** instead. Use as many parentheses as you can possibly stand, didn’t get the right results with r / (1+m**2)**(1/2) . This was changed to (r/((1+m**2)**(.5))) and it worked perfectly. And did you notice my Quadratic Bezier Curve?