# Interactive Polygons

Play with a polygon! Try adding or subtracting points.

See the lengths, angles and coordinates, from triangles on up.

images/area-coords.js

*Note: due to computer rounding errors the last digit is not always correct.*

### Edit

Use the "Edit" button to manually edit the coordinates, or to **enter new coordinates of your own**.

## What is Regular, Concave, Complex?

When all angles are equal and all sides are equal it is **regular**, otherwise it is** irregular**

When any internal angle is greater than 180° (it points inwards) then it is **concave**. (*Think: concave has a "cave" in it*), otherwise it is **convex**.

And a **complex** polygon intersects itself (the boundary crosses over), otherwise it is **simple** (like most polygons we deal with). Many rules about polygons don't work when they are complex.