Question

求函数y=cosx-3/cos+3的值域

Answer 1

由题知,

y*(cosx+3)=cosx-3

则：cosx=-3(y+1)/(y-1)

由cosx的取值范围知：-1≤cosx≤1

所以-1≤-3(y+1)/(y-1) ≤1

由-3(y+1)/(y-1)≥-1解得y≥-2

由-3(y+1)/(y-1)≤1解得y≤-1/2

则其值域为：-2≤y≤-1/2