Page 2
For more notes, call 8130648819
If x e,then the ratio test fails
Now,put x e,in equation ( )
u
u
.
n
/
.
n
/
e
Since,the expression
u
u
involves the number e,so we apply logarithmic test
log
u
u
(n )log(
n
) (n )log(
n
) log e
(n )[log(
n
) log(
n
)]
(n )[(
n
n
n
) (
n
n
n
)]
(n )[
n
n
]
n
n
n
n
n
lim
log
u
u
lim
n[
n
n
] lim
(
n
)
y logarithm test,the series diverges
Hence,the given series ?u
converges if x e and diverges if x e
Ex Discuss the convergence of the series x
x
x
x
x
Solution u
n
x
n
and u
(n )
(n )
x
u
u
n
x
n
(n )
(n )
x
n
n
(n )n
(n )
x
.
n
/
x
( )
lim
u
u
ex
4 lim
(
n
)
e5
y D
Alembert
s Ratio Test,the series
{
converges if
ex
,i e x
e
and
diverges if
ex
i e x
e
If x
e
,then Ratio test fails
Put x
e
,in equation ( )
u
u
.
n
/
e
Since,
u
u
involves the number e,we apply logarithm test
log
u
u
loge nlog(
n
)
n(
n
n
n
)
n
n
lim
[nlog
u
u
] lim
(
n
)
y Logarithm test,the series is divergent
Hence,the given series ?u
converges if x
e
and diverges if x
e
Ex Discuss the convergence of the series
x
x
x
x
Solution Here
u
n
x
n
Page 3
For more notes, call 8130648819
If x e,then the ratio test fails
Now,put x e,in equation ( )
u
u
.
n
/
.
n
/
e
Since,the expression
u
u
involves the number e,so we apply logarithmic test
log
u
u
(n )log(
n
) (n )log(
n
) log e
(n )[log(
n
) log(
n
)]
(n )[(
n
n
n
) (
n
n
n
)]
(n )[
n
n
]
n
n
n
n
n
lim
log
u
u
lim
n[
n
n
] lim
(
n
)
y logarithm test,the series diverges
Hence,the given series ?u
converges if x e and diverges if x e
Ex Discuss the convergence of the series x
x
x
x
x
Solution u
n
x
n
and u
(n )
(n )
x
u
u
n
x
n
(n )
(n )
x
n
n
(n )n
(n )
x
.
n
/
x
( )
lim
u
u
ex
4 lim
(
n
)
e5
y D
Alembert
s Ratio Test,the series
{
converges if
ex
,i e x
e
and
diverges if
ex
i e x
e
If x
e
,then Ratio test fails
Put x
e
,in equation ( )
u
u
.
n
/
e
Since,
u
u
involves the number e,we apply logarithm test
log
u
u
loge nlog(
n
)
n(
n
n
n
)
n
n
lim
[nlog
u
u
] lim
(
n
)
y Logarithm test,the series is divergent
Hence,the given series ?u
converges if x
e
and diverges if x
e
Ex Discuss the convergence of the series
x
x
x
x
Solution Here
u
n
x
n
For more notes, call 8130648819
and u
(n )
x
(n )
u
u
n
x
n
(n )
(n )
x
(n )n
(n )
x
n
.
n
/
n
.
n
/
x
.
n
/
.
n
/
x
lim
u
u
ex
y D
Alembert
s ratio test,the series converges if
ex
i e x
e
and diverges if
ex
i e x
e
if x
e
,the test fails
Now,put x
e
in equation ( )
u
u
.
n
/
e
Since,the expression for
u
u
involves the number e,we apply logarithm test
log
u
u
loge (n )log(
n
)
(n )[
n
n
n
]
n[
n
n
n
]
n
n
(
n
n
)
n
n
n
n
lim
nlog
u
u
lim
[
n
]
y logarithm test,the series converges
Hence,the given series converges if x
e
and diverges if x
e
Ex Discuss the convergence of the series
a x
(a x )
(a x )
Solution Here
u
(a nx)
n
and u
,a (n )x-
(n )
u
u
(n )
n
(a nx)
,a (n )x-
(n ) n
x
.
a
nx
/
(n )
x
[
a
(n )x
]
.
a
nx
/
.
n
/
[
a
(n )x
]
x
( )
lim
u
u
e
/
e e
/
x
ex
[ lim
.
p
n
/
e
]
y D
Alembert
s Ratio Test,the series conveges if
ex
i e x
e
and diverges if
ex
i e if x
e
If x
e
,the Ratio test fails
Put x
e
in ( ) we get
Page 4
For more notes, call 8130648819
If x e,then the ratio test fails
Now,put x e,in equation ( )
u
u
.
n
/
.
n
/
e
Since,the expression
u
u
involves the number e,so we apply logarithmic test
log
u
u
(n )log(
n
) (n )log(
n
) log e
(n )[log(
n
) log(
n
)]
(n )[(
n
n
n
) (
n
n
n
)]
(n )[
n
n
]
n
n
n
n
n
lim
log
u
u
lim
n[
n
n
] lim
(
n
)
y logarithm test,the series diverges
Hence,the given series ?u
converges if x e and diverges if x e
Ex Discuss the convergence of the series x
x
x
x
x
Solution u
n
x
n
and u
(n )
(n )
x
u
u
n
x
n
(n )
(n )
x
n
n
(n )n
(n )
x
.
n
/
x
( )
lim
u
u
ex
4 lim
(
n
)
e5
y D
Alembert
s Ratio Test,the series
{
converges if
ex
,i e x
e
and
diverges if
ex
i e x
e
If x
e
,then Ratio test fails
Put x
e
,in equation ( )
u
u
.
n
/
e
Since,
u
u
involves the number e,we apply logarithm test
log
u
u
loge nlog(
n
)
n(
n
n
n
)
n
n
lim
[nlog
u
u
] lim
(
n
)
y Logarithm test,the series is divergent
Hence,the given series ?u
converges if x
e
and diverges if x
e
Ex Discuss the convergence of the series
x
x
x
x
Solution Here
u
n
x
n
For more notes, call 8130648819
and u
(n )
x
(n )
u
u
n
x
n
(n )
(n )
x
(n )n
(n )
x
n
.
n
/
n
.
n
/
x
.
n
/
.
n
/
x
lim
u
u
ex
y D
Alembert
s ratio test,the series converges if
ex
i e x
e
and diverges if
ex
i e x
e
if x
e
,the test fails
Now,put x
e
in equation ( )
u
u
.
n
/
e
Since,the expression for
u
u
involves the number e,we apply logarithm test
log
u
u
loge (n )log(
n
)
(n )[
n
n
n
]
n[
n
n
n
]
n
n
(
n
n
)
n
n
n
n
lim
nlog
u
u
lim
[
n
]
y logarithm test,the series converges
Hence,the given series converges if x
e
and diverges if x
e
Ex Discuss the convergence of the series
a x
(a x )
(a x )
Solution Here
u
(a nx)
n
and u
,a (n )x-
(n )
u
u
(n )
n
(a nx)
,a (n )x-
(n ) n
x
.
a
nx
/
(n )
x
[
a
(n )x
]
.
a
nx
/
.
n
/
[
a
(n )x
]
x
( )
lim
u
u
e
/
e e
/
x
ex
[ lim
.
p
n
/
e
]
y D
Alembert
s Ratio Test,the series conveges if
ex
i e x
e
and diverges if
ex
i e if x
e
If x
e
,the Ratio test fails
Put x
e
in ( ) we get
For more notes, call 8130648819
u
u
e.
ae
n
/
.
ae
n
/
.
n
/
log
u
u
[loge nlog(
n
)] 0nlog.
ae
n
/ (n )log.
ae
n
/1
n(
n
n
n
)
6n4
ae
n
a
e
n
a
e
n
5 (n )8
ae
n
a
e
(n )
a
e
(n )
9 7
(
n
n
) 64
a
e
n
a
e
n
5 4
a
e
(n )
a
e
(n )
57
nlog
u
u
(
) 4
a
e
a
e
n
5
n
n
4
a
e
a
e
(n )
5
lim
[n log
u
u
]
a
e
a
e
y logtest,the series diverges
Hence,the given series converges if x
e
and diverges if x
e
Ex Discuss the convergence of the series
Solution Here
u
( n )
( n )
and u
( n )
( n )
( n )
( n )
u
u
( n )
( n )
n
.
n
/
n
.
n
/
.
n
/
.
n
/
lim
u
u
Now,the ratio test fails
n(
u
u
) n6
( n )
( n )
7
n6
n
n ( n
n )
( n )
7
n
( n )
( n )
n
n
( n )
n
.
n
/
lim
(
u
u
)
Raabe
s test also fails Now,we apply Gauss test
u
u
( n )
( n )
.
n
/
.
n
/
(
n
)
(
n
)
(
n
n
) (
n
n
)
n
n
(
)
n
n
n
O(
n
)
Comparing it with
u
u
n
O(
n
),
we have
Thus,by Gauss test,the series ?u
diverges
Que framing ta e n
term numerator as product of odd and denominator as product of even
Page 5
For more notes, call 8130648819
If x e,then the ratio test fails
Now,put x e,in equation ( )
u
u
.
n
/
.
n
/
e
Since,the expression
u
u
involves the number e,so we apply logarithmic test
log
u
u
(n )log(
n
) (n )log(
n
) log e
(n )[log(
n
) log(
n
)]
(n )[(
n
n
n
) (
n
n
n
)]
(n )[
n
n
]
n
n
n
n
n
lim
log
u
u
lim
n[
n
n
] lim
(
n
)
y logarithm test,the series diverges
Hence,the given series ?u
converges if x e and diverges if x e
Ex Discuss the convergence of the series x
x
x
x
x
Solution u
n
x
n
and u
(n )
(n )
x
u
u
n
x
n
(n )
(n )
x
n
n
(n )n
(n )
x
.
n
/
x
( )
lim
u
u
ex
4 lim
(
n
)
e5
y D
Alembert
s Ratio Test,the series
{
converges if
ex
,i e x
e
and
diverges if
ex
i e x
e
If x
e
,then Ratio test fails
Put x
e
,in equation ( )
u
u
.
n
/
e
Since,
u
u
involves the number e,we apply logarithm test
log
u
u
loge nlog(
n
)
n(
n
n
n
)
n
n
lim
[nlog
u
u
] lim
(
n
)
y Logarithm test,the series is divergent
Hence,the given series ?u
converges if x
e
and diverges if x
e
Ex Discuss the convergence of the series
x
x
x
x
Solution Here
u
n
x
n
For more notes, call 8130648819
and u
(n )
x
(n )
u
u
n
x
n
(n )
(n )
x
(n )n
(n )
x
n
.
n
/
n
.
n
/
x
.
n
/
.
n
/
x
lim
u
u
ex
y D
Alembert
s ratio test,the series converges if
ex
i e x
e
and diverges if
ex
i e x
e
if x
e
,the test fails
Now,put x
e
in equation ( )
u
u
.
n
/
e
Since,the expression for
u
u
involves the number e,we apply logarithm test
log
u
u
loge (n )log(
n
)
(n )[
n
n
n
]
n[
n
n
n
]
n
n
(
n
n
)
n
n
n
n
lim
nlog
u
u
lim
[
n
]
y logarithm test,the series converges
Hence,the given series converges if x
e
and diverges if x
e
Ex Discuss the convergence of the series
a x
(a x )
(a x )
Solution Here
u
(a nx)
n
and u
,a (n )x-
(n )
u
u
(n )
n
(a nx)
,a (n )x-
(n ) n
x
.
a
nx
/
(n )
x
[
a
(n )x
]
.
a
nx
/
.
n
/
[
a
(n )x
]
x
( )
lim
u
u
e
/
e e
/
x
ex
[ lim
.
p
n
/
e
]
y D
Alembert
s Ratio Test,the series conveges if
ex
i e x
e
and diverges if
ex
i e if x
e
If x
e
,the Ratio test fails
Put x
e
in ( ) we get
For more notes, call 8130648819
u
u
e.
ae
n
/
.
ae
n
/
.
n
/
log
u
u
[loge nlog(
n
)] 0nlog.
ae
n
/ (n )log.
ae
n
/1
n(
n
n
n
)
6n4
ae
n
a
e
n
a
e
n
5 (n )8
ae
n
a
e
(n )
a
e
(n )
9 7
(
n
n
) 64
a
e
n
a
e
n
5 4
a
e
(n )
a
e
(n )
57
nlog
u
u
(
) 4
a
e
a
e
n
5
n
n
4
a
e
a
e
(n )
5
lim
[n log
u
u
]
a
e
a
e
y logtest,the series diverges
Hence,the given series converges if x
e
and diverges if x
e
Ex Discuss the convergence of the series
Solution Here
u
( n )
( n )
and u
( n )
( n )
( n )
( n )
u
u
( n )
( n )
n
.
n
/
n
.
n
/
.
n
/
.
n
/
lim
u
u
Now,the ratio test fails
n(
u
u
) n6
( n )
( n )
7
n6
n
n ( n
n )
( n )
7
n
( n )
( n )
n
n
( n )
n
.
n
/
lim
(
u
u
)
Raabe
s test also fails Now,we apply Gauss test
u
u
( n )
( n )
.
n
/
.
n
/
(
n
)
(
n
)
(
n
n
) (
n
n
)
n
n
(
)
n
n
n
O(
n
)
Comparing it with
u
u
n
O(
n
),
we have
Thus,by Gauss test,the series ?u
diverges
Que framing ta e n
term numerator as product of odd and denominator as product of even
For more notes, call 8130648819
Ex Discuss the convergence of the series
Solution Neglecting the first term,we have
u
( n )
( n )
and u
( n )
( n )
( n )
( n )
u
u
( n )
( n )
.
n
/
.
n
/
lim
u
u
Ratio test fails
Now,
u
u
(
n
)
(
n
)
(
n
n
) (
n
n
) (on expanding by inomial Theorem)
n
n
n
n
n
n
n
n
O(
n
)
Comparing it with
u
u
n
O(
n
),
we have
y Gauss test, the series ?u
diverges
Ex Test for convergence of the positive term series
( )( )
( )( )
Solution Neglecting the first terms,we have
u
( )( ) (n )
( )( ) (n )
and u
( )( ) (n )(n )
( )( ) (n )(n )
u
u
(n )
(n )
n
n
lim
u
u
The Ratio test fails
Now,
u
u
(
n
) (
n
)
(
n
) (
n
)
n
O(
n
)
y Gauss test,the series is convergent if ,i e and divergent if ,i e if
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