.
x1=x2; x1=0到90


2
m l x2 sin(2 x1 )
m1 g sin(x1) - -----------------------
2 - u cos (x1)
x2 =------------------------------------------------
4 m1 l
-------------------------------------
2
3- m cos (x1)
m=0.1
m1=1.1
l=0.5
g= 9.8

这个式子怎么写啊, 求高手指教,要快,谢谢