=(sinx+cosx)^2+2cos^x =2+sin2x+cos2x =2+√2sin(2x+π/4) y max=2+√2,y min=2-√2.2kπ+π/2≤2x+π/4≤2kπ+3π/2 2kπ+π/4≤2x≤2kπ+5π/4 kπ+π/8≤x≤kπ+5π/8 它的递减区间[kπ+π/8,kπ+5π/8],k∈Z....