f(cosx+sinx)=sinxcosx,则f(cos(π/6))=?

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f(cosx+sinx)=sinxcosx,则f(cos(π/6))=?
f(cosx+sinx)=sinxcosx,则f(cos(π/6))=?

f(cosx+sinx)=sinxcosx,则f(cos(π/6))=?
令sinx+cosx=t
平方1+2sinxcosx=t²
sinxcosx=(t²-1)/2
f(t)=(t²-1)/2
f(cos(π/6))=f(√3/2)=[(√3/2)²-1]/2=-1/8

(cosx+sinx)^2=1+2sinxcosx,令cosx+sinx=t,则sinxcosx=(t^2-1)/2,故f(t)=(t^2-1)/2
当t=cos(π/6)=√3/2时,f(cos(π/6))=-1/8