(π/4+kπ,3π/4+kπ)(k∈z)
对于函数y=f(x)=sin2x,当2x∈(π/2+2kπ,3π/2+2kπ)(k∈z)时f(x)单调递减,解得x∈(π/4+kπ,3π/4+kπ)(k∈z)时f(x)单调递减,即函数y=sin2x的单调递减区间是单调递减区间为(π/4+kπ,3π/4+kπ)(k∈z)