c299792458
Jul31-11, 11:01 AM
Hi, why is it true that for \vec{x^\varepsilon}=\frac{\vec{x(t)}-\varepsilon \vec{y(t)}}{|\vec{x(t)}-\varepsilon \vec{y(t)}|},
\frac{\partial}{\partial x} |\vec{\dot{x}}|^2=-2 |\vec{\dot{x}}|^2 \vec{x} at \varepsilon=0?
Thanks.
\frac{\partial}{\partial x} |\vec{\dot{x}}|^2=-2 |\vec{\dot{x}}|^2 \vec{x} at \varepsilon=0?
Thanks.