Calculate ∇ · D at the point specified if

(a) D = (1/z²)[10xyz a_x + 5x²z a_y + (2z³ − 5x² y) a_z] at P(−2, 3, 5);

(b) D = 5z² a_ρ + 10ρz a_z at P(3,−45◦, 5);

(c) D = 2r sin θ sin ϕ a_r + r cos θ sin ϕ a_θ + r cos ϕ a_ϕ at P(3, 45◦, −45◦).