令t=π/3-2x、那么y=3sint的增区间为[2kπ-π/2,2kπ+π/2],k∈Z 所以π/3-2x在区间[2kπ-π/2[2kπ+π/2],所以x的单调增区间为[-π/12-kπ,5π/12-kπ],同理减区间为[-7π/12-kπ,-π/12-kπ]