Exercise 23

Use the Chain Rule to find the indicated partial derivatives. \(w = xy + yz + zx\), \(x = r \cos \theta\), \(y = r \sin \theta\), \(z = r\theta\); find \(\frac{\partial w}{\partial r}\), \(\frac{\partial w}{\partial \theta}\) when \(r = 2, \theta = \pi/2\).