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我們老師用的無(wú)窮小的等價(jià)代換
：老師有問(wèn)題
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等價(jià)的條件是aX+b趨于0還是sin(aX+b)趨于0