∵2sinxcosx=sin2x,cos²x—sin²x=cos2x
∴f（x)=cos²x+2sinxcosx—sin²x
=sin2x+cos2x
=√2(√2/2sin2x+√2/2cos2x)
=√2sin(2x+π/4)
f(x)的最小正周期T=2π/2=π

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