x+4/π∈[-π/2+2kπ,π/2+2kπ] 增区间
解得x∈[-3π/4+2kπ,π/4+2kπ]增区间
x+4/π∈[π/2+2kπ,3π/2+2kπ] 减区间
解得x∈[π/4+2kπ,5π/4+2kπ]减区间