f(x)=(cosx)^2-cosx-1=(cosx-1/2)^2-5/4
对选项坦丛喊扮A x∈(π/3,2π/3),cosx∈(-1/2,1/2)为减函数而且f(x)在(-1/2,1/2)也为减函数,由复合函数同增异减的性质,f(x)在(π/3,2π/3)为增让渗樱函数 选A