若3sinacosa=0
若3sina-cosa=0,则cos^2a 1/2sin2a=
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.
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=3/5 cos^2a +1/2sin2a=26/15
答:6sin²a+sinacosa-2cos²a=0 解:(2sina-cosa)(3sina+2cosa)=0 2sina-cosa=0或3s...详情>>
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