Geoboard

Geoboard:

Buttons:

0=0 Insert new rubber band

T Erase rubber band

Col Change rubber band color

A Calculate area

Drag vertices and edges.

Drag all mesh touching thumbtacks.

Zoom mesh with 'pinch zoom'.

Menu:

Square or isometric mesh.

Practice:

Calculate area contained inside the rubber band (only in square mesh).

Pick's Theorem:

A = I + B/2 -1

A = Area

I = Inner dots.

B = Border dots.

Convex, concave polygons, positive or negative areas:

Triangles

Rectangles

Squares

Tilted rectangles

Tilted squares

Tilted triangles

Farey Sunburst