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The Unit Circle

Know where your angles are...

Know

sin goes up and down, cos goes back and forth , short = ( 1 / 2 ) , medium = ( square root( 2 ) / 2 ) , long = ( square root( 3 ) / 2 )


And it's easy to remember the lengths at the  90 degrees angles:

unit circle's 90 degree angles ... ( 1 , 0 ) , ( 0 , 1 ) , ( -1 , 0 ) , ( 0 , -1 )
 

All you really need are the sines and cosines because you can get all the others from these using basic identities:

tan( theta ) = ( sin( theta ) / cos( theta ) )   cot( theta ) = ( cos( theta ) / sin( theta ) )
sec( theta ) = ( 1 / cos( theta ) )   csc( theta ) = ( 1 / sin( theta ) )


When you need to figure something out, just get in the habit of drawing a little unit circle.  Works every time!