n+p
n+p
cos k
cos n
n(n+1)
Pn=1
cos n
n(n+1)
Pn=1
1√n
Pn=1
n+p
Pk=n+1
n+p
Pk=n+1
1
k(k+1) =
k+1 ) = 1
cos k
k(k+1)| ≤
n+1 − 1
n+p+1 < 1
Pk=n+1
Pk=n+1
n+p
( 1
k − 1
k(k+1)| < 1
5êÆ61›S‰
SSS10.1
1.|^…Âñy²:
(1)?ê ∞
Âñ.
y. |
n .é
?¿ε > 0, N = [ 1
ε ],n > Nž, |
n < ε.d…Âñ,
?ê ∞
Âñ.
(2)?ê ∞
Ñ.
1√k| ≥ p√n+p . NõŒ,n = p = N + 1ž, |
y.
.d…Âñ,?ê ∞
Ñ.
(3) ‡?ê ∞
an† ∞
bnÑÂñ,…3êN ,n ≥ Nžkan ≤
un ≤ bn,?ê ∞
unǑÂñ.
an† ∞
y.é?¿ε > 0,ÏǑ?ê ∞
bnÂñ,¤±3N′ > N ,
n > N′ž, |
bk| < ε. ¡,
uk| < ε.¤±?ê ∞
unÂñ.
bk.¤±
2.®?ê ∞
anÂñ,?ê ∞
bn Ñ,¯?ê ∞
(an ± bn) ÄÂñ?
‰: Ñ.Ä ∞
(an ± bn)ǑÂñ.
3.äe?ê ÄÂñ.
√k) = √n + 1− 1,3n → ∞
(√n + 1−√n).ÏǑ© n
ž
vk4,¤±?ê Ñ.
(2n−1)(2n+1) .ÏǑ n
žk4,¤±?êÂñ.
3n → ∞
n = 1,¤±?ê Ñ.
n .ÏǑ lim
Pk=n+1
|
q N +1
2 ≥ 1√2
Pk=n+1
Pk=n+1
|
Pn=1
Pk=n+1
n+p
(√k + 1−
(2k−1)(2k+1) =
Pn=1
an ±
1
2k−1 − 1
2k+1 ) = 1
2 (1− 1
2n+1 ),
Pn=1
Pn=1
ak| < ε, |
Pk=n+1
ak ≤
Pk=n+1
Pn=1
bn = ±
n+p
Pk=n+1
n+p
Pk=n+1
1√n
Pn=1
n
Pk=1
1
2 (
1√k| ≥
∞
Pn=1
(4)
cos2 π
n+p
n+p
Pk=1
1
(1)
(2)
n+p
n+p
uk ≤
Pn=1
∞
Pn=1
1
Pk=1
Pn=1
Pn=1
Pn=1
Pn=1
∞
Pn=1
∞
Pn=1
∞
Pn=1
cos2 π
n→∞
1
n→∞
Pn=1
n→∞
Pn=1
Pn=1
n→∞
nun = 0.
lim
n→∞
(7)
∞
Pn=1
{S2n}
{S2n+1}
n+p
Pk=n+1
S2n = lim
n→∞
n√0.0001.ÏǑ lim
n√0.0001 = 1,¤±?ê Ñ.
4.?ê ∞
un©SǑ
{Sn}.en → ∞
ž
†
ÑÂñ…Â
ñÓ‡~êA.y²?ê ∞
unÂñ.
S2n+1 = A,¤±3N > 0,
y.é?¿ε > 0,ÏǑ lim
n > Nž, |S2n − A| < ε, |S2n+1 − A| < ε. n > Nž, |Sn − A| < ε.¤
± lim
unÂñ.
Sn = A,?ê ∞
5.?ê ∞
unÂñ,…un ≥ un+1 ≥ 0 (n = 1, 2, . . . ),y²:
y.é?¿ε > 0,ÏǑ?ê ∞
unÂñ,d…Âñ,3N ,
n > Nž,
2 . n > Nž, (2n)u2n ≤ 2
uk < ε.¤± lim
SSS10.2
1.? e?êñÑ5.
2n = π,?ê ∞
4n .ÏǑ lim
Âñ,¤±?êÂñ.
Âñ,¤±?êÂ
.ÏǑ lim
,?ê ∞
ñ.
n√n = 1,¤±?ê Ñ.
n√n .ÏǑ lim
Ñ,¤±?ê Ñ.
n = 4,?ê ∞
n2+4n−3 .ÏǑ lim
.ÏǑ lim
Âñ,¤±?êÂñ.
2 ,?ê ∞
(ln n)ln n .ÏǑ lim
(3 − ln ln n) ln n = −∞,¤
± lim
n2 = 0.?ê ∞
Âñ,¤±?êÂñ.
3 ,d…{,?êÂñ.
3n .ÏǑ lim
2.? e?êñÑ5.
Pn=1
/ 1
n2 = lim
n→∞
∞
Pn=1
∞
Pn=1
∞
Pn=1
1
n2
Pn=1
nqn tan 1
(2n + 1)u2n+1 ≤
(1 + 3n+1
n2 )− n+2
n2 ] = lim
n→∞
Pn=1
Pn=1
1√2n3+1
/ 1√n3 = 1√2
4n
n2+4n−3 / 1
∞
Pn=1
∞
Pn=1
n→∞
∞
Pn=1
ln[
n
(ln n)ln n / 1
2n sin π
4n / 1
n
(ln n)ln n / 1
2n+1
Pk=n+1
2n
Pk=n+1
2n
Pk=n+1
(n2+3n+1)
n+2
2
(n2+3n+1)
n+2
2
(5)
e− 3
(7)
n tan 1
(6)
∞
Pn=2
(1)
(2)
(3)
(4)
1
n2
Pn=1
n
n→∞
1
1
4n
1
2n
1√n3
nun = 0.
n→∞
2n sin π
1√2n3+1
un < ε
uk +
nn
nn
n→∞
n→∞
n→∞
n→∞
uk < ε.
n→∞
2 =
1
n
Pn=1
Pn=1
n→∞
3n = 1
2
3(1 + 1
n→∞
n→∞
1
n
Pn=1
n5
n!
3n·n!
1
n→∞
n→∞
n!
n→∞
n→∞
n→∞
1000n
n!
(n!)2
n2
(3− 1
n
(1)
(2)
(3)
(4)
(5)
(6)
(7)
(8)
1
n1+1/n / 1
n )n = 1
(n+1)5
(n+1)! / n5
nn = lim
n→∞
3n+1·(n+1)!
(n+1)n+1 / 3n·n!
∞
Pn=1
∞
Pn=1
∞
Pn=1
∞
Pn=1
∞
Pn=1
∞
Pn=2
∞
Pn=1
∞
Pn=1
∞
Pn=1
∞
Pn=2
nq n2
(3− 1
nq n
1000n+1
(n+1)! / 1000n
n! .ÏǑ lim
n! = 0,dˆ{,?êÂñ.
3n2 .ÏǑ lim
3n2 = +∞,?ê Ñ.
nn .ÏǑ lim
n )−n = 3e−1 > 1,dˆ
{,?ê Ñ.
n1+1/n .ÏǑ lim
n = 1,?ê ∞
Ñ,¤±?ê Ñ.
n )n .ÏǑ lim
3 ,d…{,?êÂñ.
(ln n)n .ÏǑ lim
(ln n)n = 0,d…{,?êÂñ.
n! = 0,dˆ{,?êÂñ.
.ÏǑ lim
4 ,dˆ{,?êÂñ.
(2n)! .ÏǑ lim
.ÏǑ lim
3 < 1,d…{,?êÂñ.
n(ln n)p (p > 0).p > 1ž,È©
Âñ,¤
±?êÂñ.p = 1ž,È©
Ñ,¤±?ê Ñ.
Ñ,¤±?ê Ñ.
0 < p < 1ž,È©
n(ln ln n)q (q > 0).ÏǑ lim
Ñ,¤±?ê Ñ.
(ln x)q = +∞.?ê ∞
unÂñ,?ê ∞
3.y²:e?ê ∞
ǑÂñ.‡ƒ ¤ ,Á~
`².y.ÏǑ?ê ∞
un = 0,¤±S
unÂñ,¤± lim
k..un < M .
n ≤ M un.d{,?ê ∞
Âñ.
u2
Ñ.
n )2Âñ, ∞
‡ƒ ¤ ,~X?ê ∞
Ǒ
4.y²:e?ê ∞
† ∞
ÑÂñ,?ê ∞
Âñ.y.d^‡,?ê ∞
n)Âñ.d
x(ln x)p = ln ln x|+∞2
x(ln x)p = (ln x)1−p
1−p
x(ln x)p = (ln x)1−p
1−p
n(ln n)1/2 = lim
n→∞
(2n+2)! / (n!)2
((n+1)!)2
(2n)! = 1
3n ( n+1
n )n2 = e
n→∞
Pn=1
Pn=1|anbn|,
(ln n)1/2
(ln ln n)q =
1
3n ( n+1
n )n2
1
n(ln ln n)q /
lim
x→+∞
|anbn| ≤ 1
2 (a2
n + b2
n), (an + bn)2 ≤
(an+bn)2,
a2
n
Pn=1
u2
n
Pn=1
∞
Pn=1
|an|n
b2
n
Pn=1
( 1
Pn=1
1
n(ln n)1/2
(a2
n + b2
(9)
(10)
R +∞
2
1
R +∞
2
1
R +∞
2
1
(11)
∞
Pn=3
nq 1
n→∞
1
1
1
n
Pn=1
|+∞2
1
Pn=3
Pn=1
{un}
∞
Pn=1
x1/2
n→∞
|+∞2
n→∞
Pn=1
Pn=1
u2
n
3
2(a2
n + b2
∞
Pn=1
n→∞
(1)
(2)
Pn=1
∞
Pn=1
Pn=1
n
Pn=1
n
Pn=1
∞
Pn=1
unvn.
|an|n
Pn=1
(1)
(un + vn); (2)
Pn=1|anbn|,
Pn=1
∞
Pn=1
(un − vn); (3)
n),¤±?ê ∞
n ,=Ñ?
(an + bn)2ǑÂñ.bn = 1
Âñ.
ê ∞
5.y²:e?ê ∞
vnÑÂñ,¯e?ê Ä Ñ?
un† ∞
‰. (1) Ñ,ÏǑun + vn ≥ un,Šâ{,?ê ∞
(un + vn) Ñ.
(2) ,Xun = vn = 1
ž,?ê ∞
(un − vn)Âñ0. (3) ,
unvnÂñ.
Xun = vn = 1
ž,?ê ∞
un Ñ.
6. lim
nun = l,¥0 < l < +∞.y²?ê ∞
Âñ, ∞
nun = l > 0¿›Xn¿©Œžun > 0.¤±Œ±bun > 0.Ï
y.Äk lim
Âñ.ÏǑ lim
n2 = l2,?ê ∞
Âñ,¤±?ê ∞
Ǒ lim
?ê ∞
Ñ,¤±?ê ∞
un Ñ.
SSS10.3
1.äe?ê ÄÂñ?^‡Âñ„ éÂñ?
.ÏǑ ∞
Âñ,¤±?êéÂñ.
(2n−1)p (p > 0).S
ª 0,¤±T†?êÂñ.?
…=p > 1žÂñ,¤±?êp > 1žéÂñ,Ä^‡
ê ∞
Âñ.
n ln n .S
ª 0,¤±T†?êÂñ. ?ê ∞
Ñ,¤±?ê^‡Âñ.
n .ª=
n , ‡†?êÑÂ
n / 1√n = 1,¤±?ê ∞
ñ,¤±?êÂñ. lim
Ñ.¤±
?ê^‡Âñ.
32n+1 = 0.dˆ{,
3n2 .ÏǑ lim
?êéÂñ.
Pn=1| (−1)n−1
{
(−1)n 1√n −
√n−1
∞
Pn=1
∞
Pn=1
Pn=1
(−1)n √n−1
3n2 = lim
n→∞
n→∞
Pn=1
(n+1)!
3(n+1)2 / n!
Pn=1
Pn=1
(−1)n n!
1
(2n−1)p }
1
n ln n
Pn=2
∞
Pn=1
| =
∞
Pn=1
(−1)n 1
(3)
∞
Pn=2
(4)
∞
Pn=1
(6)
∞
Pn=1
√n−1
n
Pn=1
(−1)n−1
(2n)2
(−1)n+1
∞
Pn=1
n→∞
1
(2n−1)p
(−1)n
un/ 1
n = l,
n→∞
n→∞
n/ 1
u2
1
n
u2
n
Pn=1
Pn=1
(2n)2
1
(2n)2
1
n2
u2
n
Pn=1
n→∞
n+1
{ 1
n ln n}
4
Pn=1
sin
Pn=1
Pn=1
n
(10)
∞
Pn=1
n
Pn=1
(7)
(8)
un
np
Pn=1
{ n
n+1}
n→∞
un
1
n sin π
n / 1
∞
Pn=2
∞
Pn=1
π√n2+1+n
/ 1
n = π
{ 1
np }
Pn=1
n (− π
| tan ϕ
n|
n→∞| tan ϕ
n|/ 1
n→∞
2 < ϕ < π
n sin π
(−1)n 1
(−1)n+1 tan ϕ
n = |ϕ|,
sin(π√n2 + 1). sin(π√n2 + 1) = (−1)n sin π(√n2 + 1−n) = (−1)n sin
n2 = π,¤±?êéÂñ.
n .ÏǑ lim
2 ).ϕ = 0ž,?êwéÂñ.ÄT?
ª 0,Ïd?êÂñ. lim
êǑ†?ê,…
?ê éÂñ.
2 ,?ê éÂñ.
ÏdT?êǑÂñ†?ê. lim
2.®?ê ∞
unÂñ,y²?ê ∞
np (p > 0)† ∞
n+1 unÂñ.
unÂñ,dC{,?
k.,ÏǑ?ê ∞
y.ê
9
ê ∞
† ∞
n+1 unÂñ.
(0 < ϕ < 2π)p > 1žéÂñ,0 < p ≤ 1ž^‡Â
3.y²?ê ∞
ñ.y. (i)p > 1ž,?ê ∞
Âñ.d
np ,?ê ∞
é
cos kϕk.,d
Âñ. (ii)0 < p ≤ 1.d ê
ª 0,© n
|ŽX{,?ê ∞
Âñ.ÓŒyϕ 6= πž,?ê ∞
Âñ.
Ñ.ÏǑ
d ?ê ∞
Ñ,¤±?ê ∞
,?ê ∞
éÂñ.
?ꡊ|ŽX?ê.y²§ke5Ÿ:e?ê ∞
5./X ∞
Â
ñ( Ñ),x > x0(x < x0)ž,?ê ∞
ǑÂñ( Ñ).
k..dC{,
y.?ê ∞
Âñ.x > x0ž,ê
?ê ∞
nx0 nx0−xÂñ.
n unǑéÂñ.
unéÂñ,y²?ê ∞
6.?ê ∞
y. | 2n−1
ǑÂñ.
n un| ≤ 2|un|,¤±?ê ∞
Âñ¿›X?ê ∞
SSS10.4
Pn=1
| ≥ cos2 nϕ
| cos nϕ
Pn=1
Pn=1|un|
| cos nϕ
np
| ≤ 1
Pn=1
an
nx =
an
nx0
∞
Pn=1
Pn=1
2n−1
n |un|
{nx0−x}
an
nx
Pn=1
an
nx
Pn=1
1
np
Pn=1
1
2np
Pn=1
an
nx0
Pn=1
1+cos 2nϕ
2np
1+cos 2nϕ
2np
cos nϕ
np
Pn=1
cos nϕ
np
Pn=1
cos nϕ
np
Pn=1
cos nϕ
np
Pn=1
np
np =
{ 1
np }
Pn=1
Pn=1
an
Pk=1
cos 2nϕ
2np
π√n2+1+n
.
Pn=1
2n−1
5
3
π
|x| >
xn sin π
3 ) ∪ ( 1
1
xn sin π
lim
n→∞
(1) fn(x) = 1
(1)
(2)
(3)
1
3
∞
Pn=1
∞
Pn=1
∞
Pn=1
1
2n−1 ( 1−x
1
xn sin π
2n+x2 , −∞ < x < +∞.
lim
n→∞
|fn(x) − 0| ≤ 1
(2) fn(x) = √x4 + e−n, −∞ < x < +∞.
|x| ≤ 1
3n | ≤ 1
|x|n
3 , +∞).
1.e?êÂñ.
| ln x| < 1ž?êÂñ,¤±ÂñǑ(e−1, e).
(ln x)n.…=
1+x )n.…= 1−x
1+x ∈ [−1, 1)ž?êÂñ,¤±ÂñǑ(0, +∞).
ž,
3n 6= 0,¤±?ê Ñ.
3n .
3n ,d{Œ,?êéÂñ.¤±Âñ
ž, | 1
Ǒ(−∞,− 1
2.? eêS3¤««SÂñ5.
.
2n ,… lim
2n = 0,¤±êSÂ
fn(x) = 0.d
ñ.
fn(x) = √x4 = x2.d
.
… lim
2 = 0,¤±êSÂñ.
fn(x) = 0. (a)d
.
n2 ,… lim
n2 = 0,¤±êS
3«(−l, l)Âñ. (b)xn = n, lim
[f (xn) − 0] = ln 2¤±ê
S3«(−∞, +∞) Âñ.
¤±êS
.
fn(x) = 1.xn = 1
n2 , lim
Âñ.
3.? e?ê3¤««Âñ5.
. |(−1)n √n
n3/2 ,dM{,?êÂñ.
n = 0,¤±?êÂñ.
. |
n3 ,dM{,?êÂñ.
. |
(−1)n √n
x2+n2| ≤
n − xn+1
( xn
n+1 ), −1 ≤ x ≤ 1.
k+1 )| = | xn+1
k − xk+1
( xk
n2 ), (a) −l < x < +l, (b) −∞ < x < +∞.
√1+(x2+n2)3 , −∞ < x < +∞.
x2+n2 , −∞ < x < +∞.
e−n
√x4+e−n+x2 ≤ e−n
√e−n = e− n
2 ,
[f (xn) − 1] = − 1
2
|fn(x) − 0| ≤ x2
n2 < l2
(4) fn(x) = n2x
1+n2x , 0 < x < 1.
∞
Pn=1
∞
Pk=n+1
∞
Pn=1
√1+(x2+n2)3 | ≤ 1
∞
Pn=1
sin nx
sin nx
x
1+4n4x2 , −∞ < x < +∞.
n+1 | ≤ 1
n ,
1
lim
n→∞
(3) fn(x) = ln(1 + x2
|fn(x) − x2| =
lim
n→∞
e− n
n→∞
(1)
∞
Pn=1
√n
n2 = 1
(3)
(4)
lim
n→∞
lim
n→∞
l2
n→∞
n→∞
(2)
1
n→∞
n→∞
6
1
n
Pk=1
∞
Pn=1
(6)
(7)
(5)
x2
lim
n→∞
|
1+nx ≤ 1
n ,
x2
(1+x)k = x
x
1+4n4x2| ≤ 1
|
, −∞ < x < +∞.
sin x · sin kx| = | cos x
2 − cos(n + 1
2 )x]| ≤ 2,
sin x·sin nx
√n2+x2 , 0 ≤ x ≤ 2π.
1√n2+x2}
{
2 · [cos x
∞
(−1)n−1x2e−nx2
Pn=1
∞
Pk=n+1
(−1)k−1x2e−kx2
∞
Pn=1
(1+x)n , −∞ < x < +∞.
∞
(1+x)n ≤ x
Pk=n+1
∞
Pn=1
1√n2+x2 ≤ 1
n ,
4n2 ,dM{,?êÂñ.
. 1 + 4n4x2 ≥ 4n2|x|,¤±
n = 0,¤±?êÂñ.
.
Âñ0.Ï
.
n = 0,¤±êS
Ǒ 1√n2+x2
n ,…
Šâ|ŽX{,?êÂñ.
. |
n = 0,¤±?
êÂñ.
3−n sin 2nx3(−∞, +∞)¥Âñ,…këY
4.y²?êf (x) =
ê.y. (i) |3−n sin 2nx| ≤ 3−n,ŠâM{,?ê ∞
3−n sin 2nxÂñ.
3 )n,ŠâM{,?ê ∞
(3−n sin 2nx)′
Âñ. f (x)këYê.
3(−∞, +∞)¥ Âñ,3?¿4«
5.y²?êg(x) =
[−M, M ] (M > 0)Âñ,¿y²g(x)3(−∞, +∞)¥këYê.
y.
3k | ≥ 2n+1 sin 1 > sin 1,¤±?ê
(i)xn = 3n+1,
3(−∞, +∞)¥ Âñ.
(ii)x ∈ [−M, M ]ž, |2n sin x
3 )n.ŠâM{,?
34«[−M, M ]Âñ.
ê ∞
3 )n,ŠâM{,?ê ∞
3n )′3
«(−∞, +∞)Âñ. g(x)3«(−∞, +∞)këYê.
6.y²?êζ(x) =
3?¿«[1 + δ, +∞)¥Âñ(δ > 0),¿y²?
3?¿«[1+δ, +∞)¥Âñ(δ > 0), Ñêζ(x)3(1, +∞)¥
ê ∞
këYê.
(ii) |(3−n sin 2nx)′| = |( 2
| = x2e−nx2
ex2 +1 ≤ x2e−nx2
(iii) |(2n sin x
3n )′| = |( 2
3n| ≤ |2n · x
3n | ≤ M ( 2
3 )n cos 2nx| ≤ ( 2
3 )n cos x
3n | ≤ ( 2
∞
Pk=n+1
|
2n sin x
3n
Pn=1
∞
Pn=1
1
nx
≤ e−1
n ,
lim
n→∞
e−1
(2n sin x
Pn=1
∞
Pn=1
2n sin x
3n
Pn=1
Pn=1
ln n
nx
Pn=1
1
lim
n→∞
2k sin xn
7
1
nx
Pn=1
∞
Pn=1
( 1
nx )′ =
x→0+0
ln n
nx
Pn=1
Pn=1
an
nx
Pn=1
ln n
ln n
∞
Pn=1
∞
Pn=1
nx ≤ 1
∞
Pn=1
− ln n
∞
Pn=1
an
nx =
n1+δ ≤ M
(ii) lim
n→∞
nx ≤ ln n
y. (i)x ∈ [1 + δ, +∞]ž, 1
n1+δ ,ŠâM{,?ê ∞
3«[1 +
δ, +∞)¥Âñ.
nδ/2 = 0,¤±3M > 0, ln n
nδ/2 < M . x ∈ [1 + δ, +∞]ž,
n1+δ/2 ,ŠâM{,?ê ∞
3«[1 + δ, +∞)¥Âñ.
(iii)¤ã,3?¿«(1+δ, +∞), ζ(x)këYêζ′(x) =
nx .¤±ζ′(x)3«(1, +∞)ëY.
8. ∞
3[0, +∞)¥Âñ,¿k lim
anÂñ.y²?ê ∞
n ,… 1
an.y.x ∈ [0, +∞)ž,
nx ≤ 1.d ∞
anÂñ,ŠâC
3[0, +∞)¥Âñ. lim
{,?ê ∞
an.SSS10.5
1.e?êÂñŒ.
2 ,ÂñŒǑ2.
n+1 = 0,ÂñŒǑ+∞.
n )−n = e−1,ÂñŒǑe.
4 ,ÂñŒǑ4.
2.e?êÂñ«†Âñ.
3√n = 1,Âñ«Ǒ(−1, 1).x = 1ž?ê Ñ,
x = −1ž†?êÂñ,¤±ÂñǑ[−1, 1).
a ,Âñ«Ǒ(−a, a).x = až?ê
Ñ, x = −až†?êÂñ,¤±ÂñǑ[−a, a).
(2n+1)·(2n+1)! = 0,Âñ«
ÂñǑ(−∞, +∞).
∞
Pn=1
∞
Pn=1
∞
Pn=1
∞
Pn=1
n )k ·
(1 + 1
(n+1)2n+1 / 1
n2n = 1
|x2n+3|
(2n+3)·(2n+3)! /
(n+1)2
(2n+1)(2n+2) = 1
(2n)! = lim
n→∞
((n+1)!)2
(2n+2)! / (n!)2
x2n+1
(2n+1)·(2n+1)! .
nn = lim
n→∞
n! = lim
n→∞
xn
nan (a > 0).
nq 1
nan = 1
lim
n→∞
lim
n→∞
∞
Pn=0
(−1)n
Pn=1
∞
Pn=1
(n+1)!
(n+1)n+1 / n!
(1)
(2)
(3)
(4)
∞
Pn=1
∞
Pn=1
lim
x→0+0
an
nx =
xn
n2n .
lim
n→∞
(n+1)k
(n+1)! / nk
an
nx =
∞
Pn=1
xn
3√n .
lim
n→∞
nk
n! xn.
n!
nn xn.
(1)
(2)
(3)
(1 + 1
1
(n!)2
(2n)! xn.
lim
n→∞
1
3√n+1 / 1
lim
n→∞
1
nx
1
lim
n→∞
|x2n+1|
an
nx
Pn=1
x→0+0
8