Fuente TeX:

\\\frac{d(\dot{\theta}^2)}{dt}=2\dot{\theta}\ddot{\theta}\\ \frac{d}{dt}\left(\frac{d\theta}{dt}\right)^2=2\frac{d\theta}{dt}\frac{d\dot{\theta}}{dt}\\ \frac{d}{dt}\left(\frac{d\theta}{dt}\frac{d\theta}{dt}\right)=2\frac{d\theta}{dt}\frac{d}{dt}\left(\frac{d\theta}{dt}\right)\\ \frac{d}{dt}\frac{d\theta}{dt}\frac{d\theta}{dt}=2\frac{d\theta}{dt}\frac{d}{dt}\frac{d\theta}{dt}\\ \frac{d^2\theta}{dt^2}\frac{d\theta}{dt}=2\frac{d\theta}{dt}\frac{d^2\theta}{dt^2}\\\dot{\theta}\ddot{\theta}=2 \dot{\theta}\ddot{\theta}\\0=\dot{\theta}\ddot{\theta}\Rightarrow \dot{\theta}=0\vee \ddot{\theta}=0