1.12.5 Vector analysis

Problem: Calculate the gradient of the scalar field \( \varphi(x, y, z) \), find and draw level surfaces \[ \varphi=0 ; \pm 1 ; \pm 3, \quad \text { where } \quad \varphi(x, y, z)=\frac{12 z}{x^{2}+y^{2}} . \]