Page 1
Edurev123
Complex Analysis
1. Analytic Functions
1.1 Let ?? (?? )=
?? ?? +?? ?? ?? +?.+?? ?? -?? ?? ?? -?? ?? ?? +?? ?? ?? +?.+?? ?? ?? ?? ,?? ?? ??? . Assume that the zeroes of the denominator
are simple. Show that the sum of the residues of ?? (?? ) at its poles is equal to
?? ?? -?? ?? ?? .
(2009 : 12 Marks)
Solution:
Proof: As the zeroes of denominator are simple, so ?? 0
+?? 1
?? +?..+?? ?? ?? ?? can be written
as
?? ?? (?? -?? 0
)(?? -?? 1
)(?? -?? 2
)…(?? -?? ?? -1
)
or
As maximum degree of ' ?? ' in numerator is ?? -1 and degree of denominator is ?? (i.e.,
degree of denominator is greater than degree of numerator).
So, ?? (?? ) can be written as
?? (?? )=
?? 0
?? -?? 0
+
?? 1
?? -?? 1
+
?? 2
?? -?? 2
+?…
?? ?? -1
?? -?? ?? -1
(2)
=
?? 0
(?? -?? 1
)(?? -2)·….(?? -?? ?? -1
)+?? 1
(?? -?? 0
)(?? -?? 2
)-(?? -?? ?? -1
)+??? ?? (?? -?? 0
)(?? -?? ?? -2
)
(?? -?? 0
)(?? -?? 1
)…..(?? -?? ?? -1
)
(3)
Now, we know that residues of ?? (?? ) are ?? 0
,?? 1
,?? 2
,….,?? ?? -1
.
According to problem, we need to calculate ?? 0
+?? 1
+?? 2
…..?? ?? -1
.
From (3), the coefficient of ?? ?? -1
in numerator will be calculated as :
?? 0
+?? 1
+?? 2
…..?? ?? -1
because on observing
?? 0
(?? -?? 1
)(?? -?? 2
)-(?? -?? ?? -1
)
+?? 1
(?? -?? 0
)(?? -?? 2
)-(?? -?? ?? -1
)
+?? 2
(?? -?? 0
)(?? -?? 1
)(?? -?? 3
)-(?? -?? ?? -1
)
+??
+?? ?? -1
(?? -?? 0
)(?? -?? 1
)….(?? -?? ?? -2
)
Page 2
Edurev123
Complex Analysis
1. Analytic Functions
1.1 Let ?? (?? )=
?? ?? +?? ?? ?? +?.+?? ?? -?? ?? ?? -?? ?? ?? +?? ?? ?? +?.+?? ?? ?? ?? ,?? ?? ??? . Assume that the zeroes of the denominator
are simple. Show that the sum of the residues of ?? (?? ) at its poles is equal to
?? ?? -?? ?? ?? .
(2009 : 12 Marks)
Solution:
Proof: As the zeroes of denominator are simple, so ?? 0
+?? 1
?? +?..+?? ?? ?? ?? can be written
as
?? ?? (?? -?? 0
)(?? -?? 1
)(?? -?? 2
)…(?? -?? ?? -1
)
or
As maximum degree of ' ?? ' in numerator is ?? -1 and degree of denominator is ?? (i.e.,
degree of denominator is greater than degree of numerator).
So, ?? (?? ) can be written as
?? (?? )=
?? 0
?? -?? 0
+
?? 1
?? -?? 1
+
?? 2
?? -?? 2
+?…
?? ?? -1
?? -?? ?? -1
(2)
=
?? 0
(?? -?? 1
)(?? -2)·….(?? -?? ?? -1
)+?? 1
(?? -?? 0
)(?? -?? 2
)-(?? -?? ?? -1
)+??? ?? (?? -?? 0
)(?? -?? ?? -2
)
(?? -?? 0
)(?? -?? 1
)…..(?? -?? ?? -1
)
(3)
Now, we know that residues of ?? (?? ) are ?? 0
,?? 1
,?? 2
,….,?? ?? -1
.
According to problem, we need to calculate ?? 0
+?? 1
+?? 2
…..?? ?? -1
.
From (3), the coefficient of ?? ?? -1
in numerator will be calculated as :
?? 0
+?? 1
+?? 2
…..?? ?? -1
because on observing
?? 0
(?? -?? 1
)(?? -?? 2
)-(?? -?? ?? -1
)
+?? 1
(?? -?? 0
)(?? -?? 2
)-(?? -?? ?? -1
)
+?? 2
(?? -?? 0
)(?? -?? 1
)(?? -?? 3
)-(?? -?? ?? -1
)
+??
+?? ?? -1
(?? -?? 0
)(?? -?? 1
)….(?? -?? ?? -2
)
In each of terms respectively coefficient of ?? ?? -1
will be ?? 0
,?? 1
,?? 2
…..?? ?? -1
. So, the overall
coefficient of ?? ?? -1
in numerator will be ?? 0
+?? 1
+?? 2
…..?? ?? -1
.
Now, comparing this coefficient of 2
?? -1
with (1) i.e.,
?? 0
?? ?? +
?? 1
?? ?? ?? +
?? 2
?? ?? ?? 2
….·
?? ?? -1
?? ?? ?? ?? -1
(?? -?? 0
)(?? -?? 1
)….(?? -?? ?? -1
)
(4)
In this fraction, coefficient of ?? ?? -1
will be
?? ?? -1
?? ?? .
(as denominator (?? -?? 0
)(?? -?? 1
)…..(?? -?? ?? -1
) is common (3) and (4))
??????????????????????????????????? 0
+?? 1
+?? 2
…?? ?? -1
=
?? ?? -1
?? ??
or Sum of residues =
?? ?? -1
?? ?? . Thus Proved.
1.2 Show that ?? (?? ,?? )=?? ?? -?? ?? +?? ?? ?? ?? is a harmonic function. Find a harmonic
conjugate of ?? (?? ,?? ) . Hence, find the analytic function ?? for which ?? (?? ,?? ) is the real
part.
(2010 : 12 Marks)
Solution:
Given
?? (?? ,?? )?=2?? -?? 3
+3?? ?? 2
??? ??? ?=2-3?? 2
+3?? 2
,
?
2
?? ??? 2
=-6?? ??? ??? ?=6???? ,
?
2
?? ??? 2
=6??
???????????????????????????????????????????
?
2
?? ??? 2
+
?
2
?? ??? 2
=-6?? +6?? =0
??? (?? ,?? ) is a harmonic function.
Let ?? be its harmonic conjugate.
Page 3
Edurev123
Complex Analysis
1. Analytic Functions
1.1 Let ?? (?? )=
?? ?? +?? ?? ?? +?.+?? ?? -?? ?? ?? -?? ?? ?? +?? ?? ?? +?.+?? ?? ?? ?? ,?? ?? ??? . Assume that the zeroes of the denominator
are simple. Show that the sum of the residues of ?? (?? ) at its poles is equal to
?? ?? -?? ?? ?? .
(2009 : 12 Marks)
Solution:
Proof: As the zeroes of denominator are simple, so ?? 0
+?? 1
?? +?..+?? ?? ?? ?? can be written
as
?? ?? (?? -?? 0
)(?? -?? 1
)(?? -?? 2
)…(?? -?? ?? -1
)
or
As maximum degree of ' ?? ' in numerator is ?? -1 and degree of denominator is ?? (i.e.,
degree of denominator is greater than degree of numerator).
So, ?? (?? ) can be written as
?? (?? )=
?? 0
?? -?? 0
+
?? 1
?? -?? 1
+
?? 2
?? -?? 2
+?…
?? ?? -1
?? -?? ?? -1
(2)
=
?? 0
(?? -?? 1
)(?? -2)·….(?? -?? ?? -1
)+?? 1
(?? -?? 0
)(?? -?? 2
)-(?? -?? ?? -1
)+??? ?? (?? -?? 0
)(?? -?? ?? -2
)
(?? -?? 0
)(?? -?? 1
)…..(?? -?? ?? -1
)
(3)
Now, we know that residues of ?? (?? ) are ?? 0
,?? 1
,?? 2
,….,?? ?? -1
.
According to problem, we need to calculate ?? 0
+?? 1
+?? 2
…..?? ?? -1
.
From (3), the coefficient of ?? ?? -1
in numerator will be calculated as :
?? 0
+?? 1
+?? 2
…..?? ?? -1
because on observing
?? 0
(?? -?? 1
)(?? -?? 2
)-(?? -?? ?? -1
)
+?? 1
(?? -?? 0
)(?? -?? 2
)-(?? -?? ?? -1
)
+?? 2
(?? -?? 0
)(?? -?? 1
)(?? -?? 3
)-(?? -?? ?? -1
)
+??
+?? ?? -1
(?? -?? 0
)(?? -?? 1
)….(?? -?? ?? -2
)
In each of terms respectively coefficient of ?? ?? -1
will be ?? 0
,?? 1
,?? 2
…..?? ?? -1
. So, the overall
coefficient of ?? ?? -1
in numerator will be ?? 0
+?? 1
+?? 2
…..?? ?? -1
.
Now, comparing this coefficient of 2
?? -1
with (1) i.e.,
?? 0
?? ?? +
?? 1
?? ?? ?? +
?? 2
?? ?? ?? 2
….·
?? ?? -1
?? ?? ?? ?? -1
(?? -?? 0
)(?? -?? 1
)….(?? -?? ?? -1
)
(4)
In this fraction, coefficient of ?? ?? -1
will be
?? ?? -1
?? ?? .
(as denominator (?? -?? 0
)(?? -?? 1
)…..(?? -?? ?? -1
) is common (3) and (4))
??????????????????????????????????? 0
+?? 1
+?? 2
…?? ?? -1
=
?? ?? -1
?? ??
or Sum of residues =
?? ?? -1
?? ?? . Thus Proved.
1.2 Show that ?? (?? ,?? )=?? ?? -?? ?? +?? ?? ?? ?? is a harmonic function. Find a harmonic
conjugate of ?? (?? ,?? ) . Hence, find the analytic function ?? for which ?? (?? ,?? ) is the real
part.
(2010 : 12 Marks)
Solution:
Given
?? (?? ,?? )?=2?? -?? 3
+3?? ?? 2
??? ??? ?=2-3?? 2
+3?? 2
,
?
2
?? ??? 2
=-6?? ??? ??? ?=6???? ,
?
2
?? ??? 2
=6??
???????????????????????????????????????????
?
2
?? ??? 2
+
?
2
?? ??? 2
=-6?? +6?? =0
??? (?? ,?? ) is a harmonic function.
Let ?? be its harmonic conjugate.
?
??? ??? =
??? ??? =2-3?? 2
+3?? 2
? ?? =2?? -3?? 2
?? +?? 3
+?? (?? )
Also,
??? ??? =-
??? ??? =6????
?
??? ??? =-6????
? ?? =-3?? 2
?? +?? (?? )…(2)(?? (?? ) and ?? (?? ) are some arbitrary functions)
(1)
Comparing (1) and (2), we get
Now, let
?? ?=2?? +?? 3
-3?? 2
?? +?? , where ?? is a constant.
?? ?=?? (?? ,?? )+???? (?? ,?? )
?? ?=(2?? -?? 3
+3?? ?? 2
)+??(2?? +?? 3
-3?? 2
?? +?? )
?? (?? )?=??(?? 1
(?? ,0)-???? 2
(?? ,0))????
?=??(2-3?? 2
)???? =2?? -?? 3
+?? , where ?? is a constant
???? ?=(2?? -?? 3
+3)
?? (?? )?=??(?? 1
(?? ,0)-?? ?=??(2-3?? 2
)?? ???? (?? )?=2?? -?? 3
+??
1.3 (i) Evaluate the line integral ?
?? ??? (?? )???? where ?? (?? )=?? ?? ,?? is the boundary of the
triangle with vertices ?? (?? ,?? ),?? (?? ,?? ),?? (?? ,?? ) in that order.
(ii) Find the image of the finite vertical strip ?? : ?? =?? to ?? =?? ,-?? =?? =?? of ?? -
plane under exponential function.
(2010 : 15 Marks)
Solution:
(i) Given: ?? (?? )=?? 2
Now, ?? (?? )=?? 2
is analytic in whole given region.
Line integral of cled boundary curve of analytic function is always zero.
??
?? ??? (?? )???? in the given region is 0 .
(ii) Given : ?? varies from 5 to 9 and ?? varies from -?? to ?? .
Now, ??? =?? +????
Page 4
Edurev123
Complex Analysis
1. Analytic Functions
1.1 Let ?? (?? )=
?? ?? +?? ?? ?? +?.+?? ?? -?? ?? ?? -?? ?? ?? +?? ?? ?? +?.+?? ?? ?? ?? ,?? ?? ??? . Assume that the zeroes of the denominator
are simple. Show that the sum of the residues of ?? (?? ) at its poles is equal to
?? ?? -?? ?? ?? .
(2009 : 12 Marks)
Solution:
Proof: As the zeroes of denominator are simple, so ?? 0
+?? 1
?? +?..+?? ?? ?? ?? can be written
as
?? ?? (?? -?? 0
)(?? -?? 1
)(?? -?? 2
)…(?? -?? ?? -1
)
or
As maximum degree of ' ?? ' in numerator is ?? -1 and degree of denominator is ?? (i.e.,
degree of denominator is greater than degree of numerator).
So, ?? (?? ) can be written as
?? (?? )=
?? 0
?? -?? 0
+
?? 1
?? -?? 1
+
?? 2
?? -?? 2
+?…
?? ?? -1
?? -?? ?? -1
(2)
=
?? 0
(?? -?? 1
)(?? -2)·….(?? -?? ?? -1
)+?? 1
(?? -?? 0
)(?? -?? 2
)-(?? -?? ?? -1
)+??? ?? (?? -?? 0
)(?? -?? ?? -2
)
(?? -?? 0
)(?? -?? 1
)…..(?? -?? ?? -1
)
(3)
Now, we know that residues of ?? (?? ) are ?? 0
,?? 1
,?? 2
,….,?? ?? -1
.
According to problem, we need to calculate ?? 0
+?? 1
+?? 2
…..?? ?? -1
.
From (3), the coefficient of ?? ?? -1
in numerator will be calculated as :
?? 0
+?? 1
+?? 2
…..?? ?? -1
because on observing
?? 0
(?? -?? 1
)(?? -?? 2
)-(?? -?? ?? -1
)
+?? 1
(?? -?? 0
)(?? -?? 2
)-(?? -?? ?? -1
)
+?? 2
(?? -?? 0
)(?? -?? 1
)(?? -?? 3
)-(?? -?? ?? -1
)
+??
+?? ?? -1
(?? -?? 0
)(?? -?? 1
)….(?? -?? ?? -2
)
In each of terms respectively coefficient of ?? ?? -1
will be ?? 0
,?? 1
,?? 2
…..?? ?? -1
. So, the overall
coefficient of ?? ?? -1
in numerator will be ?? 0
+?? 1
+?? 2
…..?? ?? -1
.
Now, comparing this coefficient of 2
?? -1
with (1) i.e.,
?? 0
?? ?? +
?? 1
?? ?? ?? +
?? 2
?? ?? ?? 2
….·
?? ?? -1
?? ?? ?? ?? -1
(?? -?? 0
)(?? -?? 1
)….(?? -?? ?? -1
)
(4)
In this fraction, coefficient of ?? ?? -1
will be
?? ?? -1
?? ?? .
(as denominator (?? -?? 0
)(?? -?? 1
)…..(?? -?? ?? -1
) is common (3) and (4))
??????????????????????????????????? 0
+?? 1
+?? 2
…?? ?? -1
=
?? ?? -1
?? ??
or Sum of residues =
?? ?? -1
?? ?? . Thus Proved.
1.2 Show that ?? (?? ,?? )=?? ?? -?? ?? +?? ?? ?? ?? is a harmonic function. Find a harmonic
conjugate of ?? (?? ,?? ) . Hence, find the analytic function ?? for which ?? (?? ,?? ) is the real
part.
(2010 : 12 Marks)
Solution:
Given
?? (?? ,?? )?=2?? -?? 3
+3?? ?? 2
??? ??? ?=2-3?? 2
+3?? 2
,
?
2
?? ??? 2
=-6?? ??? ??? ?=6???? ,
?
2
?? ??? 2
=6??
???????????????????????????????????????????
?
2
?? ??? 2
+
?
2
?? ??? 2
=-6?? +6?? =0
??? (?? ,?? ) is a harmonic function.
Let ?? be its harmonic conjugate.
?
??? ??? =
??? ??? =2-3?? 2
+3?? 2
? ?? =2?? -3?? 2
?? +?? 3
+?? (?? )
Also,
??? ??? =-
??? ??? =6????
?
??? ??? =-6????
? ?? =-3?? 2
?? +?? (?? )…(2)(?? (?? ) and ?? (?? ) are some arbitrary functions)
(1)
Comparing (1) and (2), we get
Now, let
?? ?=2?? +?? 3
-3?? 2
?? +?? , where ?? is a constant.
?? ?=?? (?? ,?? )+???? (?? ,?? )
?? ?=(2?? -?? 3
+3?? ?? 2
)+??(2?? +?? 3
-3?? 2
?? +?? )
?? (?? )?=??(?? 1
(?? ,0)-???? 2
(?? ,0))????
?=??(2-3?? 2
)???? =2?? -?? 3
+?? , where ?? is a constant
???? ?=(2?? -?? 3
+3)
?? (?? )?=??(?? 1
(?? ,0)-?? ?=??(2-3?? 2
)?? ???? (?? )?=2?? -?? 3
+??
1.3 (i) Evaluate the line integral ?
?? ??? (?? )???? where ?? (?? )=?? ?? ,?? is the boundary of the
triangle with vertices ?? (?? ,?? ),?? (?? ,?? ),?? (?? ,?? ) in that order.
(ii) Find the image of the finite vertical strip ?? : ?? =?? to ?? =?? ,-?? =?? =?? of ?? -
plane under exponential function.
(2010 : 15 Marks)
Solution:
(i) Given: ?? (?? )=?? 2
Now, ?? (?? )=?? 2
is analytic in whole given region.
Line integral of cled boundary curve of analytic function is always zero.
??
?? ??? (?? )???? in the given region is 0 .
(ii) Given : ?? varies from 5 to 9 and ?? varies from -?? to ?? .
Now, ??? =?? +????
Image under exponential function will be
?? ?? =?? ?? +????
=?? ?? ·?? ????
As ?? varies from 5 to 9,??? ?? varies from ?? 5
to ?? 9
.
Also, ?? ??4
denotes angle variation.
So, image is given by region in figure.
So, the region is bounded by two circles of radii ?? 5
and ?? 9
.
1.4 If ?? (?? )=?? +?? is an analytic function of ?? =?? +?? and ?? -?? =
?? ?? -?????? ??? +?????? ??? ???????? ??? -?????? ??? , find
?? (?? ) subject to the condition, ?? (
?? ?? )=
?? -?? ?? .
(2011 : 12 Marks)
Solution:
Page 5
Edurev123
Complex Analysis
1. Analytic Functions
1.1 Let ?? (?? )=
?? ?? +?? ?? ?? +?.+?? ?? -?? ?? ?? -?? ?? ?? +?? ?? ?? +?.+?? ?? ?? ?? ,?? ?? ??? . Assume that the zeroes of the denominator
are simple. Show that the sum of the residues of ?? (?? ) at its poles is equal to
?? ?? -?? ?? ?? .
(2009 : 12 Marks)
Solution:
Proof: As the zeroes of denominator are simple, so ?? 0
+?? 1
?? +?..+?? ?? ?? ?? can be written
as
?? ?? (?? -?? 0
)(?? -?? 1
)(?? -?? 2
)…(?? -?? ?? -1
)
or
As maximum degree of ' ?? ' in numerator is ?? -1 and degree of denominator is ?? (i.e.,
degree of denominator is greater than degree of numerator).
So, ?? (?? ) can be written as
?? (?? )=
?? 0
?? -?? 0
+
?? 1
?? -?? 1
+
?? 2
?? -?? 2
+?…
?? ?? -1
?? -?? ?? -1
(2)
=
?? 0
(?? -?? 1
)(?? -2)·….(?? -?? ?? -1
)+?? 1
(?? -?? 0
)(?? -?? 2
)-(?? -?? ?? -1
)+??? ?? (?? -?? 0
)(?? -?? ?? -2
)
(?? -?? 0
)(?? -?? 1
)…..(?? -?? ?? -1
)
(3)
Now, we know that residues of ?? (?? ) are ?? 0
,?? 1
,?? 2
,….,?? ?? -1
.
According to problem, we need to calculate ?? 0
+?? 1
+?? 2
…..?? ?? -1
.
From (3), the coefficient of ?? ?? -1
in numerator will be calculated as :
?? 0
+?? 1
+?? 2
…..?? ?? -1
because on observing
?? 0
(?? -?? 1
)(?? -?? 2
)-(?? -?? ?? -1
)
+?? 1
(?? -?? 0
)(?? -?? 2
)-(?? -?? ?? -1
)
+?? 2
(?? -?? 0
)(?? -?? 1
)(?? -?? 3
)-(?? -?? ?? -1
)
+??
+?? ?? -1
(?? -?? 0
)(?? -?? 1
)….(?? -?? ?? -2
)
In each of terms respectively coefficient of ?? ?? -1
will be ?? 0
,?? 1
,?? 2
…..?? ?? -1
. So, the overall
coefficient of ?? ?? -1
in numerator will be ?? 0
+?? 1
+?? 2
…..?? ?? -1
.
Now, comparing this coefficient of 2
?? -1
with (1) i.e.,
?? 0
?? ?? +
?? 1
?? ?? ?? +
?? 2
?? ?? ?? 2
….·
?? ?? -1
?? ?? ?? ?? -1
(?? -?? 0
)(?? -?? 1
)….(?? -?? ?? -1
)
(4)
In this fraction, coefficient of ?? ?? -1
will be
?? ?? -1
?? ?? .
(as denominator (?? -?? 0
)(?? -?? 1
)…..(?? -?? ?? -1
) is common (3) and (4))
??????????????????????????????????? 0
+?? 1
+?? 2
…?? ?? -1
=
?? ?? -1
?? ??
or Sum of residues =
?? ?? -1
?? ?? . Thus Proved.
1.2 Show that ?? (?? ,?? )=?? ?? -?? ?? +?? ?? ?? ?? is a harmonic function. Find a harmonic
conjugate of ?? (?? ,?? ) . Hence, find the analytic function ?? for which ?? (?? ,?? ) is the real
part.
(2010 : 12 Marks)
Solution:
Given
?? (?? ,?? )?=2?? -?? 3
+3?? ?? 2
??? ??? ?=2-3?? 2
+3?? 2
,
?
2
?? ??? 2
=-6?? ??? ??? ?=6???? ,
?
2
?? ??? 2
=6??
???????????????????????????????????????????
?
2
?? ??? 2
+
?
2
?? ??? 2
=-6?? +6?? =0
??? (?? ,?? ) is a harmonic function.
Let ?? be its harmonic conjugate.
?
??? ??? =
??? ??? =2-3?? 2
+3?? 2
? ?? =2?? -3?? 2
?? +?? 3
+?? (?? )
Also,
??? ??? =-
??? ??? =6????
?
??? ??? =-6????
? ?? =-3?? 2
?? +?? (?? )…(2)(?? (?? ) and ?? (?? ) are some arbitrary functions)
(1)
Comparing (1) and (2), we get
Now, let
?? ?=2?? +?? 3
-3?? 2
?? +?? , where ?? is a constant.
?? ?=?? (?? ,?? )+???? (?? ,?? )
?? ?=(2?? -?? 3
+3?? ?? 2
)+??(2?? +?? 3
-3?? 2
?? +?? )
?? (?? )?=??(?? 1
(?? ,0)-???? 2
(?? ,0))????
?=??(2-3?? 2
)???? =2?? -?? 3
+?? , where ?? is a constant
???? ?=(2?? -?? 3
+3)
?? (?? )?=??(?? 1
(?? ,0)-?? ?=??(2-3?? 2
)?? ???? (?? )?=2?? -?? 3
+??
1.3 (i) Evaluate the line integral ?
?? ??? (?? )???? where ?? (?? )=?? ?? ,?? is the boundary of the
triangle with vertices ?? (?? ,?? ),?? (?? ,?? ),?? (?? ,?? ) in that order.
(ii) Find the image of the finite vertical strip ?? : ?? =?? to ?? =?? ,-?? =?? =?? of ?? -
plane under exponential function.
(2010 : 15 Marks)
Solution:
(i) Given: ?? (?? )=?? 2
Now, ?? (?? )=?? 2
is analytic in whole given region.
Line integral of cled boundary curve of analytic function is always zero.
??
?? ??? (?? )???? in the given region is 0 .
(ii) Given : ?? varies from 5 to 9 and ?? varies from -?? to ?? .
Now, ??? =?? +????
Image under exponential function will be
?? ?? =?? ?? +????
=?? ?? ·?? ????
As ?? varies from 5 to 9,??? ?? varies from ?? 5
to ?? 9
.
Also, ?? ??4
denotes angle variation.
So, image is given by region in figure.
So, the region is bounded by two circles of radii ?? 5
and ?? 9
.
1.4 If ?? (?? )=?? +?? is an analytic function of ?? =?? +?? and ?? -?? =
?? ?? -?????? ??? +?????? ??? ???????? ??? -?????? ??? , find
?? (?? ) subject to the condition, ?? (
?? ?? )=
?? -?? ?? .
(2011 : 12 Marks)
Solution:
Let ??? (?? )=?? +????
??????? (?? )=???? -?? ???(1+??)?? (?? )=?? -?? +??(?? +?? )
?=?? +????
????? =?? -?? =
?? ?? -cos??? +sin??? cosh??? -cos??? ?=
cosh??? +sin?h?? -cos??? +sin??? cos?h?? -cos??? ?=1+
sin?h?? +sin??? cos?h?? -cos??? ??? ??? =?? 1
(?? ,?? ) and
??? ??? =?? 2
(?? ,?? )
????? 1
(?? ,?? )=
??? ??? =
cos??? (cosh??? -cos??? )-sin??? (sinh??? +sin??? )
(cosh??? -cos??? )
2
????? 1
(?? ,0)=
cos??? (1-cos??? )-sin
2
??? (1-cos??? )
2
=
cos??? -1
(1-cos??? )
2
?=
-1
1-cos??? =
-1
2
cosec
2
?
?? 2
?? 2
(?? ,?? )=
??? ??? =
cosh??? (cosh??? -cos??? )-sinh??? (sinh??? +sin??? )
(cosh??? ?cos??? )
2
?? 2
(?? ,0)=
1-cos??? (1-cos??? )
2
=
1
1-cos??
=
1
2
cosec
2
?
?? 2
? By Mine's Method
(1+??)?? (?? )?=??[?? 1
(?? ,0)-???? 2
(?? ,0)]???? +?? ?=??(-
1
2
cosec
2
?
?? 2
-?? 1
2
cosec
2
?
?? 2
)???? +?? ?=-
1
2
(1+??)??cosec
2
?
?? 2
???? +?? ?=(1+??)cot?
?? 2
+?? ???? (?? )?=cot?
?? 2
+
?? 1+?? ?=cot?
?? 2
+?? ,?? =
?? 1+?? At ?? =
?? 2
,??? (?? )?=
3-?? 2
???? ?=?? (
?? 2
)-cot?
?? 4
=
1-?? 2
???? (?? )?=cot?
?? 2
+
1-?? 2
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