Please see the attached file.
I need an explanation of how one gets from the top equation (with v)s given by to the bottom equation where v is given by l*(theta)dot. I do not need an explanation of the double pendulum.
Derive the kinetic energy equation of the double pendulum in Lagrangian.© BrainMass Inc. brainmass.com June 3, 2020, 9:56 pm ad1c9bdddf
It shows the steps of deriving the given kinetic energy equation in Lagrangian for the double pendulum.