(2cos²θ/2-1-sinθ)(√2sin(θ+π/4)=
=(cosθ-sinθ)(√2sin(θ+π/4))
=√2cos(θ＋π/4)(√2sin(θ+π/4))
=2sin(2θ+π/2)=2cos2θ
tan2θ= - 2√2
已知tan2θ=－2√2,π＜2θ＜2π,化简＜2cos²（θ/2）－sinθ－1＞＜√2sin（θ+π/4）
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