若3sina-cosa=0，则cos^2a 1/2sin2a=
热心网友
3sina-cosa=0---sina/cosa=1/3---tana=1/3---(cosa)^2=1/(seca)^2=1/[1+(tana)^2]=1/(1+1/9)=9/10---sin2a=2tana/[1+(tana)^2]=(2/3)/(1+1/9)=3/5.(cosa)^2+1/2*sin2a=9/10+3/10=6/5.
热心网友
3sina-cosa=0,tga=1/3,sin^2a=1/10,cos^2a =9/10(3sina-cosa)^2=9sin^2a+coa^2a-6sinacosa=18/10-3sin2a=0,sin2a=3/5cos^2a +1/2sin2a=26/15