分子分母倒一下
lim[x→0] (1-cosx+xsinx)/sin²x
=lim[x→0] (1-cosx+xsinx)/x²
=lim[x→0] (1-cosx)/x²+lim[x→0] xsinx/x²
=lim[x→0] (1/2)x²/x²+lim[x→0] x²/x²
=3/2
因此原题极限为：2/3