Formula_7922

\[f \equiv \sqrt{\dot{x}^{2}+\dot{y}^{2}+\dot{z}^{2}}-\varphi\left[\sqrt{\left(x-x_{1}\right)^{2}+\left(y-y_{1}\right)^{2}+\left(z-z_{1}\right)^{2}}\right]=0 .\]