y=3/2-1/2(sinx-cosx)^2=1+2sinxcosx=1+sin(2x)
∴最小正周期为π,最大值2
x∈(kπ-π/4,kπ+π/4]时,单增
x∈(kπ+π/4,kπ+3π/4]时,单减 k∈Z