A torus of radius 4 (and cross-sectional radius 1) can be represented parametrically by the function r:d→r3r:d→r3:r(θ,ϕ)=((4+cosϕ)cosθ,( 4+cosϕ)sinθ,sinϕ)r(θ,ϕ)=((4+cos⁡ϕ)c os⁡θ,(4+cos⁡ϕ)sin⁡θ,sin⁡ϕ)where d is the rectangle given by 0≤θ≤2π, 0≤ϕ≤2π0≤θ≤2π, 0≤ϕ≤2π. the surface area of the torus is