sina+cosa=1/5(sina+cosa)^2=1/25, 1+2sinacosa=1/25, sinacosa=-12/25sina+cosa=1/5, sina=1/5-cosa ,sin^2a=1/25-2/5cosa+cos^2a, cos^2a-1/5cosa-12/25, cosa=4/5 , sina-cosa=1/5-2cosa=-7/5cosa=4/5, sina=-3/5, tana=-3/4
sina+cosa=1/5(sina+cosa)^2=1/25, 1+2sinacosa=1/25, sinacosa=-12/25sina+cosa=1/5, sina=1/5-cosa ,sin^2a=1/25-2/5cosa+cos^2a, cos^2a-1/5cosa-12/25, cosa=4/5 , sina-cosa=1/5-2cosa=-7/5cosa=4/5, sina=-3/5, tana=-3/4