x->0,sinx~x
lim(x->π/2) sin6x/sin2x (0/0)
=lim(x->π/2) 6cos6x/(2cos2x)
=6/2
=3
x---＞pi/2,lim(sin6x/sin2x) ＝3我们老师用的无穷小的等价代换
：老师有问题
lim(x->π/2) sin6x/sin2x
let
y = π/2-x
x->π/2 , y->0
lim(x->π/2) sin6x/sin2x
=lim(y->0) sin(3π-6y)/sin(π-2y)
=lim(y->0) sin(6y)/sin2y
=lim(y->0) 6y/(2y)
=3那比如sin(aX+b)和aX+b等价的条件是aX+b趋于0还是sin(aX+b)趋于0