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文件名称:数列极限-模拟电路和数字电路自学手册下
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更新时间:2021-06-15 03:41:23
习题解答
1.1 数数数轴轴轴
1.2 无无无尽尽尽小小小数数数
1.3 数数数列列列极极极限限限
1.3.1 “““ε−N”””
(((1))) 1
1+
√
n
< 1√
n
< ε,,,取取取n > 1
ε2
(((2))) sinn
n
6 1
n
< ε,,,取取取n > 1
ε
(((3)))原原原式式式单单单调调调递递递减减减,,,故故故可可可取取取2n,,,
(2n)!
(2n)2n
<
nn(2n)n
(2n)2n
=
(
1
2
)n
< ε,,,由由由例例例3知知知可可可取取取n > ln ε
ln 1
2
(((4)))| (−1)
n−1
n
| < 1
n
< ε,,,取取取n > 1
ε
(((5)))| 2n+3
5n−10 −
2
5
| = | 7
5n−10 | < ε,,,取取取n >
1
5
(
7
ε
+ 10
)
(((6)))|0.9 · · · 9− 1| = 10−n < ε,,,取取取n > ln
1
ε
ln 10
(((7)))| 1+2+···+n
n2
− 1
2
| = | (n+1)n
2n2
− 1
2
| = 1
2n
< ε,,,取取取n > 1
2ε
(((8)))| 1
2+22+···+n2
n3
− 1
3
| = |n(n+1)(2n+1)
6n3
− 1
3
| = 3n
2+n
6n3
< 3n
2+n2
6n3
= 2
3n
< ε,,,取取取n > 2
3ε
(((9)))| arctann− π
2
| = π
2
− arctann < ε,,,arctann > π
2
− ε,,,取取取n > tan
(
π
2
− ε
)
(((10)))π
2
− ε < arctann
2
= n
2 arctann
n2+n2
6 n
2 arctann
1+n2
< arctann < π
2
+ ε,,,取取取n > max
{
tan (π − 2ε) , tan
(
π
2
− ε
)}
1.3.2 按按按定定定义义义;;;
||an| − |a|| 6 |an − a| < ε,即得证;逆命题不成立,如an = (−1)n
1.3.3 按按按定定定义义义;;;
取ε = 1
2
,若k ∈ (A− ε,A+ ε),则k − 1 < A− ε < k < A+ ε < k + 1,则(A− ε,A+ ε)中不含其它整数。
1.3.4 按按按定定定义义义重重重新新新叙叙叙述述述即即即可可可;;;
(((1)))不不不能能能;;;如如如{−1, 1,−1, 1, · · ·}即即即an = (−1)
n
,,,取取取a = 1
1