∵f(x)=cosx-1+cos²x=cos²x+cosx+1/4-5/4=(cosx+1/2)²-5/4又│cosx│≤1 ==>-1≤cosx≤1 ==>-1/2≤cosx+1/2≤3/2==>-3/2≤cosx+1/2≤3...