f( x) =cosx^ 2-根号3sinxcos+1 即f( x)=½cos2x-根号三/2sin2x+3/2=
-sin(2x-π/6)+3/2 单调递增区间为(kπ+π/3,kπ+5/6π)
sin2x等于(2根号3-根号5)/6