Students manipulate the angle measures (in intervals of 10 degrees) of a right triangle whose hypotenuse is 10 units. Hopefully, through careful observation and recording, they will discover the ratios that define the three basic trig functions. Then students can manipulate the size of the triangle to discover that these ratios are independent of the triangle's size, and are therefore, useful mathematical constants.
SOHCAHTOA can follow, but it shouldn't lead.
Lessons: http://bit.ly/1nT7h0t and http://bit.ly/1b1Jatx
