lim(x→∞)[(x^2-2x+1)/(x+1)直接化简即可：
lim(x→∞)[(x^2-2x+1)/(x+1)]
=lim(x→∞)[(x^2+x-3x-3+4)/(x+1)]
=lim(x→∞)[x-3+4/(x+1)]
我不知道下面这一步是怎么得来的:
=lim(x→∞)[(x^2+x-3x-3+4)/(x+1)]
=lim(x→∞)[x-3+4/(x+1)]
x^2-3x去哪里了呢?