How do I draw straight lines tangent or perpendicular to a path?

Question

The tangent is the line which is perpendicular to the local radius. Intuitively, it's the line "resting" or "balanced" on that point in the curve.The perpendicular (or the normal) is the line crossing the tangent at a right angle.How can I draw these, besides eyeballing it?

Answer 1

Difficult to do this with precision with Illustrator's native tools. Try Astute Graphics' plug-in Subscribe, it can draw precise tangents and perpendiculars to any type of curved path, at any point along it.