GeoGebra is an extremely useful tool for studying the unit circle as well as the relationship between angles and sides in a right triangle. Follow the instructions below and watch what happens! 
      
     GeoGebra Instruction 1
Algebra     View     and         Graphics     View     under         View     in         Menu.         O=(0,0)     in         Algebra     View     and         press         Enter     to         start         your         plot.         Circle     with     Center     through     Point Toolbar,         then         click         O     (origin)         in         Graphics     View.         Drag         the         circle         until         it         has         a         radius         of         1         and         click         on         the         coordinate         system.         A         point                is         now         drawn         where         you         clicked.         Segment Toolbar     and         plot         the         line         segment         from         O     (origin)         to         point                by         clicking         on         the         points.         Perpendicular     Line Toolbar     and         draw         the         normal         from                to         the         -axis         by         clicking                first,         and         then         the         -axis.         Do         the         same         with                and         the         -axis,         so         that         you         also         get         a         line         that         is         perpendicular         to         the         -axis.         Intersect Point Algebra     View.         Do         the         same         to         find         the         intersection         of         the         horizontal         line         and         the         -axis.         Angle Algebra     View.         You         can         later         click         the         dot         again         to         make         the         object         visible.         If         you         right-click         on         the         object         in         Algebra     View     you         can         change         its         properties         by         clicking         Properties.         Try         it!