1.y=cosx/(2cosx+1)求值域怎么求啊

Question

1.y=cosx/(2cosx+1)求值域
怎么求啊

Answer 1

2ycosx+y=cosx
cosx=y/(1-2y)
∴|y/(1-2y)|≤1且y/(1-2y)≠-1/2
两边平方,得：y^2≤4y^2-4y+1
3y^2-4y+1≥0
(3y-1)(y-1)≥0
∴y≥1或y≤1/3