先求y
y=limln(1+1/n(x+2))^n在n趋向于无穷大的极限
记得有个公式:1的无穷大次方求极限,如下:
y=limln[(1+1/n(x+2))^(n*(x+2))]^(1/(x+2))
=ln[lim[(1+1/n(x+2))^(n*(x+2))]^(1/(x+2))](交换lim和ln符号)
=lne^(1/(x+2))
=1/(x+2)
上面要看懂,看不懂再追问
y求出来了,y的一阶,二阶导数就好求了对吧
y'=-1/(x+2)^2
y''=[-1/(x+2)^2]'
=-[0-((x+2)^2)']/(x+2)^4
=2(x+2)/(x+2)^4
=2/(x+2)^3
上面每一步都很基础,不懂再追问吧!