On your TI-83 or 84, type 11.351 (Caution, use the POSITIVE 11.351, not -11.351)!!! press the x-1 key, read 11.351-1 press the ENTER key, read .0880970649 press the 2ND key press the COS key, read cos-1( press the 2ND key press the (-) key, read cos-1(Ans Press the ENTER key, read 84.94580618, which is in QI To get it in QII Type 180- press the 2ND key press the (-) key, read 180-Ans press the ENTER key, Read 95.05419382 press the ÷ key, read Ans/ type 2, read Ans/2 press the ENTER key, read 47.52709691 press the SIN key, read sin( press the 2ND key press the (-) key, read sin(Ans press the ENTER key, read .7375967614 Now go back and try to carefully ponder each step and figure out why we do it. Any questions?. Ask me in the thank-you note. Edwin