另π/4-2x∈〔2kπ-0.5π,2kπ+0.5π〕
则有x∈〔kπ-π/8,kπ+3π/8〕
也就是说y=2sin(π/4-2x)的单调递减区间是〔kπ-π/8,kπ+3π/8〕