y=-cos(x/2-π/3)单增区间是[4kπ+2π/3,4kπ+8/3π],k属于Z
sinα-cosα=√2/2,则(sinα-cosα)^2=1-2sinαcosα=1/2,sinαcosα=1/4
(sinα)^4+(cosα)^4=[(sinα)^2+(cosα)^2]^2-2(sinαcosα)^2=1-2*1/16=7/8