# Polar coordinate system, Archimedean spiral

**The polar coordinate system**is a two-dimensional coordinate system in which each point on a plane is determined by a distance from a reference point and an angle from a reference direction. Converting between Polar and Cartesian coordinates: Task: The curve is given by polar equation r = 2+2cos

**φ**. Determine the point with minimal curvature. First, rewrite polar coordinates to the cartesian coordinates. Instead of the greek letter

**φ**, we can use the letter

*t*. x = (2+2cos t).cos t y = (2+2cos t).sin t

Determine the point with minimal curvature (= krivost) on cardioid.

## Archimedean spiral

Start the animation of revolving parameter a (left down corner). Value of slider u specify the position of osculating circle (red).

Stop the animation and set up the trace on for osculating circle. Then change the value of parameter u on red slider.