Alternative Derivation for Pendulum Equation

https://www.youtube.com/watch?v=HPw1cqoBQZw

Here's an alternative derivation for the pendulum equation.

Fair warning though, you should not use this method of derivation if this gets asked in any exam; at least not in Nepal. The examiners will only check for specific things in your answer, and at first glance, when your answer doesn't match the rubric or the widely accepted answer, it is likely that your answer will not be marked correctly.

Now the important question: why do I even need an alternative derivation when I already know a perfectly fine derivation method?

Welp, it always helps to get different angles on a solution. You may be able to use this method of derivation in a different place, who knows. The insight is what matters.