已知向量m=(根号3sinx/4,1),n=(cosx/4,cos的平方x/4),f(x)=m*n

f(x)=cos(π/3-x/2)+1/2
f(x)=cos(π/3-x/2)+1/2=1
cos(π/3-x/2)=1/2
cos(2π/3-x)=-1/2
f(B)=cos(π/3-B/2)+1/2
acosC+1/2c=b
b^2+c^2-a^2=-bc
A=2π/3
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