y = sin (-2x - π/6) = - sin (2x + π/6)单调增区间：2kπ + π/2 ≤ 2x + π/6 ≤ 2kπ + 3π/22kπ + π/3 ≤ 2x ≤ 2kπ + 4π/3kπ + π/6 ≤ x ≤ kπ + 2π/3
