很明显，你会看到一个，简谐振荡。
It's clear that you're going to see a simple harmonic oscillation.
我们知道初始条件，我们知道这是简谐振荡，我们想知道，最大位移是多少。
We know the initial conditions, and we know it's a simple harmonic oscillation, and we want to know what the maximum displacement is going to be.
以前算过-,这是能量守恒，为了算出,简谐振荡的周期，我们求时间导数。
We've done this before-- this is the conservation of energy, and in order to find the period of the simple harmonic oscillation, we take the time derivative.
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