f（x）=cos^4x+2sinxcosx-sin^4x=(cos²x+sin²x)(cos²x-sin²x)+sin2x
=cos2x+sin2x
=√2sin﹙2x＋π／4﹚
∵T= 2π／2=π
∴f（x）的最小正周期为π．
题目有误吧!应该是 f（x）=cos^4x+2sinxcosx-sin^4x