由于T=2π/ω=2π/3为函数周期令－π/2≤3x+π/4≤π/2,得 -π/4≤x≤π/12即当2kπ/3-π/4≤x≤2kπ/3+π/12时,函数为增函数令π/2≤3x+π/4≤3π/2,得π/12≤x≤5π/12即当2kπ/3+π/12≤x≤2kπ/3+5π/12时,函数...