f(x)=sin(x/2-π/6+x/2)-sin(x/2-π/6-x/2)
=sin(x-π/6)+sin(π/6)
=sin(x-π/6)+1/2
f(x)=-1/6
sin(x-π/6)=1/3 cos(x-π/6)=2√2/3
cosx=cos(x-π/6)cos(π/6)-sin(x-π/6)sin(π/6)
=(2√6-1)/6
f(x)=2cos(x/2)sin(x/2-π/6) 若x∈(0,π/2) f(x)=-1/6 求cosx的值
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