①已知sinα=-3\5(3π\2

①已知sinα=-3\5(3π\2
①已知sinα=-3\5(3π\2

①已知sinα=-3\5(3π\2
①由sinα=-3/5(3π/2

3π/2<α<2π,sinα=-3/5,cosa=4/5=1-2sin^2(a/2)=2cos^(a/2)-1
sin(a/2)=√10/10,cos(a/2)=-3√10/10
cos(π\4+α\2)=cos(π/4)cos(a/2)-sin(π/4)sin(a/2)=[cos(a/2)-sin(a/2)]√2/2=-2√10/5



f(x)=-1\2sin2x+1\2 ,?-1/[2sin(2x)]+1/2,?-sin(2x)/2+1/2,?