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问题: 3道求极限的问题

1。
lim
x→0
右边是(X-SINX)/(X+SIN3X)

2。lim
n→∞
右边是[1+(X/N)]N次方

3. lim
x→∞
右边是[1-(1/X)]2X次方

要有步骤的,谢谢!

解答:

解:
1.lim[(x-sinx)/(x+sin3x)]
x→0
=lim[(1-sinx/x)/(1+sin(3x)/x)]
x→0
=[1-limsinx/x]/[1+lim3sin(3x)/(3x)],
x→0
=(1-1)/(1+3)
=0.
2.(1)若x≠0,则
lim[1+(x/n)]^n
n→∞
=lim{[1+(x/n)]^(n/x)}^x
n/x→∞
={lim[1+(x/n)]^(n/x)}^x
n/x→∞
=e^x;
(2)若x=0,则
lim[1+(x/n)]^n=1.
n→∞

3. lim[1-(1/x)]^(2x)
x→∞
=lim{[1-(1/X)]^x}^2
x→∞
={lim[1+(-1/X)]^(-x)}^(-2)
-x→∞
=e^(-2)
=1/e^2.