cosx的值域为【-1,1】函数y=acosx+b的值域为[(a+b),(-a+b)],所以a+b=1,-a+b=-3或a+b=-3,-a+b=1解得a=2,b=-1或a=-2,b=-1cos2x=2(cosx)²-1,(cosx)²的值域为[0,1]函数y=bcos2x+cosx+a变为y=-[2(cosx)²-1...