申論題

2. Use the surface integral in Stokes' Theorem to calculate the flux of the field
F = (x - y) i + (y-z) j + (z - x) k
across the surface
S:r (Φ,θ) = (2 sinΦcosθ) i + (2 sinΦsinθ) j + 2 cosΦ k, 0 ≤ Φ ≤ π/2,0 ≤ θ ≤ 2π 
in the direction of the outward unit normal n.