problem involves more than one coordinate, as most problems do, we just have to apply eq.
(6.3) to each coordinate. We will obtain as many equations as there are coordinates. Each
equation may very well involve many of the coordinates (see the example below, where both
equations involve both x and ต).
At this point, you may be thinking, That was a nice little trick, but we just got lucky
in the spring problem. The procedure won't work in a more general situation." Well, let's
see. How about if we consider the more general problem of a particle moving in an arbitrary
potential V (x) (we'll stick to one dimension for now). The Lagrangian is then