f(x)=cos(-x/2)+sin(π-x/2)
=cosx/2+sinx/2
=√2(√2/2sinx/2+√2/2cosx/2)
=√2sin(x/2+π/4)
最小正周期T=2π/(1/2)=4π
增区间[4kπ-3π/2,4kπ+π/2],k∈Z