5楼: Originally posted by feixiaolin at 2014-10-25 17:58:45
原函数为一力学问题，好像是每一项约掉了质量m
简写为  x"+ax+bx^3=0, x=x(t)
裂项， x=x1+x2
其中，x1"+a*x1=0,  x2"+b*x2^3=0
见图 4u.png,
x1=C1*exp(sqrt(a)t)+C2*exp(-sqrt(a)t)
    =C ...

2楼: Originally posted by hank612 at 2014-10-23 13:26:51
let dx/dt =p as a new variable, then \frac{d^2x}{dt^2}=p\cdot \frac{dp}{dx}
This gives  v^2=-2\frac{g}{l}(\frac{x^2}{2}-\frac{x^4}{24})+C_1

Then remaining task is an integral problem, although  ...