运用半角公式有
f(x)=2sinxcosx+2cos²x-1=sin2x+cos2x=√2sin(2x+π/4)
最小正周期=2π/2=π
令2kπ+π/2≤2x+π/4≤2kπ+3π/2,求得单调递减区间为kπ+π/8≤x≤kπ+5π/8