sinx ≥ - (√2)/2-√2/2=sin(-π/4)=sin(-3π/4)=sin(2kπ-π/4)=sin(2kπ-3π/4)即sinx≥sin(2kπ-π/4)sinx≥sin(2kπ-3π/4)sinx在(2kπ-π,2kπ-π/2)是减函数在(2kπ-π/2,2kπ)是增函数所以x∈(2kπ-π,2kπ-...