设π设π设ππsina=-4/5 ,cosa=-3/5sin^2a+sin2a/cos^2+cos2a=16/25+2x(-4/5)/(-3/5)+2x9/25-1=33/25
设ππ
sina=-4/5 ,cosa=-3/5sin^2a+sin2a/cos^2+cos2a=16/25+2x(-4/5)/(-3/5)+2x9/25-1=33/25