The domain of f(x)=cos(sinx) is
R
R+
R-
ϕ
f(x)=cos(sinx) is defined if cos(sinx)≥0----(1)
As we know, −1≤sinx≤1 for all x∈R . So, cosθ≥0
(Here, θ=sinx lies in the first and fourth quadrants)
i.e., cos(sinx)≥0 for all x
i.e., x∈R
Thus, the domain of f(x) is R .