Where exactly is the partial derivative and how do you know?

In spherical coordinates: av 1 av 1 ov ar ar + r 90 ag + r sin 8 00 and 1 d DA = 1 0Ag rz or (Ag sin 0) + r sin 9 80 r sin & do Knowing DIV = V . DV Hence, Laplace's equation is, 1 0 av ar (sin e or r sin 9 00 sin 0 00z