Unit Circle Tutorial
To Start
Construct point A at (0,0) and point B (1,0).
Rename point A as point O (because it is at the origin).
Use the circle tool, 
, to construct a circle centered at O that passes through B.
Use the zoom tool to zoom as required. 
or 
, to construct a circle centered at O that passes through B.
Use the zoom tool to zoom as required. or