Page 1
Edurev123
4. Second and Higher Order Linear
Equation with Constant coefficients
4.1 Use the method of undetermined coefficients to find the particular solution of
?? ''
+?? =?????? ?? +(?? +?? ?? )?? ??
and hence find its general solution.
(2010 : 20 Marks)
Solution:
Given equation is: ?? ''
+?? =sin ?? +(1+?? 2
)?? ??
Complementary Function (C.F.) :
The auxiliary equation is
?? 2
+1 =0??? =±?? ?? ?? =?? 1
?? ????
+?? 2
?? -????
(?? 1
,?? 2
are constants )
=?? cos ?? +?? sin ?? (?? ,?? are constants )
Particular Solution :
For this we will use method of undetermined coefficients.
As multiplicity of roots is 1 .
Let
?? ?? =?? (?? cos ?? +?? sin ?? )+(?? ?? 2
+???? +?? )?? ?? (1)
?? ?? '
= (?? cos ?? +?? sin ?? )+?? (-?? sin ?? +?? cos ?? )+(?? ?? 2
+???? +?? )?? ?? +(2???? +?? )?? ?? ?? ?? ''
= (-?? sin ?? +?? cos ?? )+(-?? sin ?? +?? cos ?? )+?? (-?? cos ?? -?? sin
?? )+(?? ?? 2
+???? +?? )?? ?? +(2???? +?? )?? ?? +(2???? +?? )?? ?? +2?? ?? ?? …(2)
? ?? ?? ''
= (-?? sin ?? +?? cos ?? )+(-?? sin ?? +?? cos ?? )+?? (-?? cos ?? -?? sin
?? )+(?? ?? 2
+???? +?? )?? ?? +(2???? +?? )?? ?? +(2???? +?? )?? ?? +2?? ?? ?? …(2)
? ?? ?? ''
+?? ?? =sin ?? +(1+?? 2
)?? ??
Using values from ( 1 ) and (2), we get
Page 2
Edurev123
4. Second and Higher Order Linear
Equation with Constant coefficients
4.1 Use the method of undetermined coefficients to find the particular solution of
?? ''
+?? =?????? ?? +(?? +?? ?? )?? ??
and hence find its general solution.
(2010 : 20 Marks)
Solution:
Given equation is: ?? ''
+?? =sin ?? +(1+?? 2
)?? ??
Complementary Function (C.F.) :
The auxiliary equation is
?? 2
+1 =0??? =±?? ?? ?? =?? 1
?? ????
+?? 2
?? -????
(?? 1
,?? 2
are constants )
=?? cos ?? +?? sin ?? (?? ,?? are constants )
Particular Solution :
For this we will use method of undetermined coefficients.
As multiplicity of roots is 1 .
Let
?? ?? =?? (?? cos ?? +?? sin ?? )+(?? ?? 2
+???? +?? )?? ?? (1)
?? ?? '
= (?? cos ?? +?? sin ?? )+?? (-?? sin ?? +?? cos ?? )+(?? ?? 2
+???? +?? )?? ?? +(2???? +?? )?? ?? ?? ?? ''
= (-?? sin ?? +?? cos ?? )+(-?? sin ?? +?? cos ?? )+?? (-?? cos ?? -?? sin
?? )+(?? ?? 2
+???? +?? )?? ?? +(2???? +?? )?? ?? +(2???? +?? )?? ?? +2?? ?? ?? …(2)
? ?? ?? ''
= (-?? sin ?? +?? cos ?? )+(-?? sin ?? +?? cos ?? )+?? (-?? cos ?? -?? sin
?? )+(?? ?? 2
+???? +?? )?? ?? +(2???? +?? )?? ?? +(2???? +?? )?? ?? +2?? ?? ?? …(2)
? ?? ?? ''
+?? ?? =sin ?? +(1+?? 2
)?? ??
Using values from ( 1 ) and (2), we get
2(-?? sin ?? +?? cos ?? )+?? (-?? cos ?? -?? sin ?? +(?? ?? 2
+???? +?? )?? ?? +(4???? +2?? )?? ?? +2?? ?? ?? +
(?? ?? 2
+???? +?? )?? ?? + ?? (?? cos ?? +?? sin ?? )=sin ?? +(1+?? 2
)?? ??
?2(-?? sin ?? +?? cos ?? )+2(?? ?? 2
+???? +?? )?? ?? +(4???? +2?? )?? ?? +2?? ?? ?? =sin ?? +(1+?? 2
)?? ??
Comparing LHS & RHS, we get
?? =0,?? =-
1
2
2?? =1??? =
1
2
2?? +4?? =0?2?? +2=0??? =-1
2?? +2?? +2?? =1?2?? -2+1=1??? =1
?? ?? =
-?? 2
cos ?? +(
?? 2
2
-?? +1)?? ??
So, general solution of given equation is
?? =?? cos ?? +?? sin ?? -
?? 2
cos ?? +(
?? 2
2
-?? +1)?? ??
4.2 Obtain the general solution of the second order ordinary differential equation
?? ''
-?? ?? '
+?? ?? =?? +?? ?? ?????? ??
where dashes denote derivatives w.r.t. ?? .
(2011 : 15 Marks)
Solution:
The given differential equation is
?? ''
+2?? +2?? =?? +?? ?? cos ??
The auxiliary equation is
?? 2
+2?? +2=0
? ?? =-1±??
? The complementary function is
?? ?? =?? -?? (?? 1
cos ?? +?? 2
sin ?? ) , where ?? 1
and ?? 2
are arbitrary constants.
For particular integral,
Page 3
Edurev123
4. Second and Higher Order Linear
Equation with Constant coefficients
4.1 Use the method of undetermined coefficients to find the particular solution of
?? ''
+?? =?????? ?? +(?? +?? ?? )?? ??
and hence find its general solution.
(2010 : 20 Marks)
Solution:
Given equation is: ?? ''
+?? =sin ?? +(1+?? 2
)?? ??
Complementary Function (C.F.) :
The auxiliary equation is
?? 2
+1 =0??? =±?? ?? ?? =?? 1
?? ????
+?? 2
?? -????
(?? 1
,?? 2
are constants )
=?? cos ?? +?? sin ?? (?? ,?? are constants )
Particular Solution :
For this we will use method of undetermined coefficients.
As multiplicity of roots is 1 .
Let
?? ?? =?? (?? cos ?? +?? sin ?? )+(?? ?? 2
+???? +?? )?? ?? (1)
?? ?? '
= (?? cos ?? +?? sin ?? )+?? (-?? sin ?? +?? cos ?? )+(?? ?? 2
+???? +?? )?? ?? +(2???? +?? )?? ?? ?? ?? ''
= (-?? sin ?? +?? cos ?? )+(-?? sin ?? +?? cos ?? )+?? (-?? cos ?? -?? sin
?? )+(?? ?? 2
+???? +?? )?? ?? +(2???? +?? )?? ?? +(2???? +?? )?? ?? +2?? ?? ?? …(2)
? ?? ?? ''
= (-?? sin ?? +?? cos ?? )+(-?? sin ?? +?? cos ?? )+?? (-?? cos ?? -?? sin
?? )+(?? ?? 2
+???? +?? )?? ?? +(2???? +?? )?? ?? +(2???? +?? )?? ?? +2?? ?? ?? …(2)
? ?? ?? ''
+?? ?? =sin ?? +(1+?? 2
)?? ??
Using values from ( 1 ) and (2), we get
2(-?? sin ?? +?? cos ?? )+?? (-?? cos ?? -?? sin ?? +(?? ?? 2
+???? +?? )?? ?? +(4???? +2?? )?? ?? +2?? ?? ?? +
(?? ?? 2
+???? +?? )?? ?? + ?? (?? cos ?? +?? sin ?? )=sin ?? +(1+?? 2
)?? ??
?2(-?? sin ?? +?? cos ?? )+2(?? ?? 2
+???? +?? )?? ?? +(4???? +2?? )?? ?? +2?? ?? ?? =sin ?? +(1+?? 2
)?? ??
Comparing LHS & RHS, we get
?? =0,?? =-
1
2
2?? =1??? =
1
2
2?? +4?? =0?2?? +2=0??? =-1
2?? +2?? +2?? =1?2?? -2+1=1??? =1
?? ?? =
-?? 2
cos ?? +(
?? 2
2
-?? +1)?? ??
So, general solution of given equation is
?? =?? cos ?? +?? sin ?? -
?? 2
cos ?? +(
?? 2
2
-?? +1)?? ??
4.2 Obtain the general solution of the second order ordinary differential equation
?? ''
-?? ?? '
+?? ?? =?? +?? ?? ?????? ??
where dashes denote derivatives w.r.t. ?? .
(2011 : 15 Marks)
Solution:
The given differential equation is
?? ''
+2?? +2?? =?? +?? ?? cos ??
The auxiliary equation is
?? 2
+2?? +2=0
? ?? =-1±??
? The complementary function is
?? ?? =?? -?? (?? 1
cos ?? +?? 2
sin ?? ) , where ?? 1
and ?? 2
are arbitrary constants.
For particular integral,
?? ?? =
?? +?? ?? cos ?? ?? 2
+2?? +2
,?? =
?? ????
=
1
?? 2
+2?? +2
?? +
1
?? 2
+2?? +2
·?? ?? cos ?? =
1
2[1+
?? 2
+2?? 2
]
]
?? +?? ?? 1
(?? +1)
2
+2(?? +1)+2
·cos ?? =
1
2
[1+
?? 2
+2?? 2
]
-1
·?? +?? ?? ·
1
?? 2
+4?? +5
·cos ?? =
1
2
[1-
?? 2
+2?? 2
]·?? +?? ?? ·
1
-1+4?? +5
·cos ?? =
1
2
[?? -1]+
?? ?? 4
·
1
?? +1
·cos ??
1
2
(?? -1)+
?? ?? 4
(?? -1)
?? 2
-1
cos ?? =
?? -1
2
+
?? ?? 4
·
(-1)
2
(-sin ?? -cos ?? )
=
?? -1
2
+
?? ?? 8
(sin ?? +cos ?? )
?? =?? ?? +?? ?? ?? =?? -?? (?? 1
cos ?? +?? 2
sin ?? )+
?? -1
2
+
?? ?? 8
(sin ?? +cos ?? )
is the required solution.
4.3 Find the general solution of the equation ?? '''
-?? ''
=???? ?? ?? +?? ?? .
(2012 : 20 Marks)
Solution:
The given equation is
?? ''
-?? ''
=12?? 2
+6?? (??)
Denote
?? ????
as Detc., the given equation reduces to
(?? 3
-?? 2
)?? =12?? 2
+?? ?? (???? )
The auxiliary equation of (ii) is :
?? 3
-?? 2
=0??? =0,0,1
4.4 Find a particular integral of
Page 4
Edurev123
4. Second and Higher Order Linear
Equation with Constant coefficients
4.1 Use the method of undetermined coefficients to find the particular solution of
?? ''
+?? =?????? ?? +(?? +?? ?? )?? ??
and hence find its general solution.
(2010 : 20 Marks)
Solution:
Given equation is: ?? ''
+?? =sin ?? +(1+?? 2
)?? ??
Complementary Function (C.F.) :
The auxiliary equation is
?? 2
+1 =0??? =±?? ?? ?? =?? 1
?? ????
+?? 2
?? -????
(?? 1
,?? 2
are constants )
=?? cos ?? +?? sin ?? (?? ,?? are constants )
Particular Solution :
For this we will use method of undetermined coefficients.
As multiplicity of roots is 1 .
Let
?? ?? =?? (?? cos ?? +?? sin ?? )+(?? ?? 2
+???? +?? )?? ?? (1)
?? ?? '
= (?? cos ?? +?? sin ?? )+?? (-?? sin ?? +?? cos ?? )+(?? ?? 2
+???? +?? )?? ?? +(2???? +?? )?? ?? ?? ?? ''
= (-?? sin ?? +?? cos ?? )+(-?? sin ?? +?? cos ?? )+?? (-?? cos ?? -?? sin
?? )+(?? ?? 2
+???? +?? )?? ?? +(2???? +?? )?? ?? +(2???? +?? )?? ?? +2?? ?? ?? …(2)
? ?? ?? ''
= (-?? sin ?? +?? cos ?? )+(-?? sin ?? +?? cos ?? )+?? (-?? cos ?? -?? sin
?? )+(?? ?? 2
+???? +?? )?? ?? +(2???? +?? )?? ?? +(2???? +?? )?? ?? +2?? ?? ?? …(2)
? ?? ?? ''
+?? ?? =sin ?? +(1+?? 2
)?? ??
Using values from ( 1 ) and (2), we get
2(-?? sin ?? +?? cos ?? )+?? (-?? cos ?? -?? sin ?? +(?? ?? 2
+???? +?? )?? ?? +(4???? +2?? )?? ?? +2?? ?? ?? +
(?? ?? 2
+???? +?? )?? ?? + ?? (?? cos ?? +?? sin ?? )=sin ?? +(1+?? 2
)?? ??
?2(-?? sin ?? +?? cos ?? )+2(?? ?? 2
+???? +?? )?? ?? +(4???? +2?? )?? ?? +2?? ?? ?? =sin ?? +(1+?? 2
)?? ??
Comparing LHS & RHS, we get
?? =0,?? =-
1
2
2?? =1??? =
1
2
2?? +4?? =0?2?? +2=0??? =-1
2?? +2?? +2?? =1?2?? -2+1=1??? =1
?? ?? =
-?? 2
cos ?? +(
?? 2
2
-?? +1)?? ??
So, general solution of given equation is
?? =?? cos ?? +?? sin ?? -
?? 2
cos ?? +(
?? 2
2
-?? +1)?? ??
4.2 Obtain the general solution of the second order ordinary differential equation
?? ''
-?? ?? '
+?? ?? =?? +?? ?? ?????? ??
where dashes denote derivatives w.r.t. ?? .
(2011 : 15 Marks)
Solution:
The given differential equation is
?? ''
+2?? +2?? =?? +?? ?? cos ??
The auxiliary equation is
?? 2
+2?? +2=0
? ?? =-1±??
? The complementary function is
?? ?? =?? -?? (?? 1
cos ?? +?? 2
sin ?? ) , where ?? 1
and ?? 2
are arbitrary constants.
For particular integral,
?? ?? =
?? +?? ?? cos ?? ?? 2
+2?? +2
,?? =
?? ????
=
1
?? 2
+2?? +2
?? +
1
?? 2
+2?? +2
·?? ?? cos ?? =
1
2[1+
?? 2
+2?? 2
]
]
?? +?? ?? 1
(?? +1)
2
+2(?? +1)+2
·cos ?? =
1
2
[1+
?? 2
+2?? 2
]
-1
·?? +?? ?? ·
1
?? 2
+4?? +5
·cos ?? =
1
2
[1-
?? 2
+2?? 2
]·?? +?? ?? ·
1
-1+4?? +5
·cos ?? =
1
2
[?? -1]+
?? ?? 4
·
1
?? +1
·cos ??
1
2
(?? -1)+
?? ?? 4
(?? -1)
?? 2
-1
cos ?? =
?? -1
2
+
?? ?? 4
·
(-1)
2
(-sin ?? -cos ?? )
=
?? -1
2
+
?? ?? 8
(sin ?? +cos ?? )
?? =?? ?? +?? ?? ?? =?? -?? (?? 1
cos ?? +?? 2
sin ?? )+
?? -1
2
+
?? ?? 8
(sin ?? +cos ?? )
is the required solution.
4.3 Find the general solution of the equation ?? '''
-?? ''
=???? ?? ?? +?? ?? .
(2012 : 20 Marks)
Solution:
The given equation is
?? ''
-?? ''
=12?? 2
+6?? (??)
Denote
?? ????
as Detc., the given equation reduces to
(?? 3
-?? 2
)?? =12?? 2
+?? ?? (???? )
The auxiliary equation of (ii) is :
?? 3
-?? 2
=0??? =0,0,1
4.4 Find a particular integral of
?? ?? ?? ?? ?? ?? +?? =?? ?? /?? ·??????
?? v?? ??
(2016: 10 marks)
Solution:
We write the given ODE as
(?? 2
+1)?? =?? ?? 2
·sin (
v3
2
?? )
P.I. =
1
?? 2
+1
(?? ?? 2
·sin
v3?? 2
)
=?? ?? 2
·
1
(?? +
1
2
)
2
+1
sin
v3
2
?? [
1
?? (?? )
?? ????
·?? =?? ????
??? ·?? (?? +?? )]
=?? ?? 2
·
1
?? 2
+?? +
5
4
·sin
v3?? 2
[?
1
?? (?? )
sin (???? )=
1
?? (-?? 2
)
sin (???? )]
=?? ?? 2
·
1
?? +
1
2
·sin
v3?? 2
=?? ?? 2
·
?? -
1
2
?? 2
-
1
4
·sin
v3?? 2
=?? ?? 2
·
?? -
1
2
-
3
4
-
1
4
·sin
v3?? 2
=?? ?? 2
·(
1
2
-?? )·sin
v3?? 2
=?? ?? 2
[
1
2
sin
v3
2
?? -
v3
2
cos
v3
2
?? ]
=?? ?? 2
·sin (
v3?? 2
-
?? 3
)
4.5 Solve: ?? ''
-?? =?? ?? ?? ?? ??
(2018 : 10 Marks)
Solution:
?????????? ?????????? ?????? ???? ?? ''
-?? =?? 2
?? 2??
or (?? 2
-1)?? =?? 2
?? 2??
C.F. : Auxiliary equation is (?? 2
-1)?? =0
Page 5
Edurev123
4. Second and Higher Order Linear
Equation with Constant coefficients
4.1 Use the method of undetermined coefficients to find the particular solution of
?? ''
+?? =?????? ?? +(?? +?? ?? )?? ??
and hence find its general solution.
(2010 : 20 Marks)
Solution:
Given equation is: ?? ''
+?? =sin ?? +(1+?? 2
)?? ??
Complementary Function (C.F.) :
The auxiliary equation is
?? 2
+1 =0??? =±?? ?? ?? =?? 1
?? ????
+?? 2
?? -????
(?? 1
,?? 2
are constants )
=?? cos ?? +?? sin ?? (?? ,?? are constants )
Particular Solution :
For this we will use method of undetermined coefficients.
As multiplicity of roots is 1 .
Let
?? ?? =?? (?? cos ?? +?? sin ?? )+(?? ?? 2
+???? +?? )?? ?? (1)
?? ?? '
= (?? cos ?? +?? sin ?? )+?? (-?? sin ?? +?? cos ?? )+(?? ?? 2
+???? +?? )?? ?? +(2???? +?? )?? ?? ?? ?? ''
= (-?? sin ?? +?? cos ?? )+(-?? sin ?? +?? cos ?? )+?? (-?? cos ?? -?? sin
?? )+(?? ?? 2
+???? +?? )?? ?? +(2???? +?? )?? ?? +(2???? +?? )?? ?? +2?? ?? ?? …(2)
? ?? ?? ''
= (-?? sin ?? +?? cos ?? )+(-?? sin ?? +?? cos ?? )+?? (-?? cos ?? -?? sin
?? )+(?? ?? 2
+???? +?? )?? ?? +(2???? +?? )?? ?? +(2???? +?? )?? ?? +2?? ?? ?? …(2)
? ?? ?? ''
+?? ?? =sin ?? +(1+?? 2
)?? ??
Using values from ( 1 ) and (2), we get
2(-?? sin ?? +?? cos ?? )+?? (-?? cos ?? -?? sin ?? +(?? ?? 2
+???? +?? )?? ?? +(4???? +2?? )?? ?? +2?? ?? ?? +
(?? ?? 2
+???? +?? )?? ?? + ?? (?? cos ?? +?? sin ?? )=sin ?? +(1+?? 2
)?? ??
?2(-?? sin ?? +?? cos ?? )+2(?? ?? 2
+???? +?? )?? ?? +(4???? +2?? )?? ?? +2?? ?? ?? =sin ?? +(1+?? 2
)?? ??
Comparing LHS & RHS, we get
?? =0,?? =-
1
2
2?? =1??? =
1
2
2?? +4?? =0?2?? +2=0??? =-1
2?? +2?? +2?? =1?2?? -2+1=1??? =1
?? ?? =
-?? 2
cos ?? +(
?? 2
2
-?? +1)?? ??
So, general solution of given equation is
?? =?? cos ?? +?? sin ?? -
?? 2
cos ?? +(
?? 2
2
-?? +1)?? ??
4.2 Obtain the general solution of the second order ordinary differential equation
?? ''
-?? ?? '
+?? ?? =?? +?? ?? ?????? ??
where dashes denote derivatives w.r.t. ?? .
(2011 : 15 Marks)
Solution:
The given differential equation is
?? ''
+2?? +2?? =?? +?? ?? cos ??
The auxiliary equation is
?? 2
+2?? +2=0
? ?? =-1±??
? The complementary function is
?? ?? =?? -?? (?? 1
cos ?? +?? 2
sin ?? ) , where ?? 1
and ?? 2
are arbitrary constants.
For particular integral,
?? ?? =
?? +?? ?? cos ?? ?? 2
+2?? +2
,?? =
?? ????
=
1
?? 2
+2?? +2
?? +
1
?? 2
+2?? +2
·?? ?? cos ?? =
1
2[1+
?? 2
+2?? 2
]
]
?? +?? ?? 1
(?? +1)
2
+2(?? +1)+2
·cos ?? =
1
2
[1+
?? 2
+2?? 2
]
-1
·?? +?? ?? ·
1
?? 2
+4?? +5
·cos ?? =
1
2
[1-
?? 2
+2?? 2
]·?? +?? ?? ·
1
-1+4?? +5
·cos ?? =
1
2
[?? -1]+
?? ?? 4
·
1
?? +1
·cos ??
1
2
(?? -1)+
?? ?? 4
(?? -1)
?? 2
-1
cos ?? =
?? -1
2
+
?? ?? 4
·
(-1)
2
(-sin ?? -cos ?? )
=
?? -1
2
+
?? ?? 8
(sin ?? +cos ?? )
?? =?? ?? +?? ?? ?? =?? -?? (?? 1
cos ?? +?? 2
sin ?? )+
?? -1
2
+
?? ?? 8
(sin ?? +cos ?? )
is the required solution.
4.3 Find the general solution of the equation ?? '''
-?? ''
=???? ?? ?? +?? ?? .
(2012 : 20 Marks)
Solution:
The given equation is
?? ''
-?? ''
=12?? 2
+6?? (??)
Denote
?? ????
as Detc., the given equation reduces to
(?? 3
-?? 2
)?? =12?? 2
+?? ?? (???? )
The auxiliary equation of (ii) is :
?? 3
-?? 2
=0??? =0,0,1
4.4 Find a particular integral of
?? ?? ?? ?? ?? ?? +?? =?? ?? /?? ·??????
?? v?? ??
(2016: 10 marks)
Solution:
We write the given ODE as
(?? 2
+1)?? =?? ?? 2
·sin (
v3
2
?? )
P.I. =
1
?? 2
+1
(?? ?? 2
·sin
v3?? 2
)
=?? ?? 2
·
1
(?? +
1
2
)
2
+1
sin
v3
2
?? [
1
?? (?? )
?? ????
·?? =?? ????
??? ·?? (?? +?? )]
=?? ?? 2
·
1
?? 2
+?? +
5
4
·sin
v3?? 2
[?
1
?? (?? )
sin (???? )=
1
?? (-?? 2
)
sin (???? )]
=?? ?? 2
·
1
?? +
1
2
·sin
v3?? 2
=?? ?? 2
·
?? -
1
2
?? 2
-
1
4
·sin
v3?? 2
=?? ?? 2
·
?? -
1
2
-
3
4
-
1
4
·sin
v3?? 2
=?? ?? 2
·(
1
2
-?? )·sin
v3?? 2
=?? ?? 2
[
1
2
sin
v3
2
?? -
v3
2
cos
v3
2
?? ]
=?? ?? 2
·sin (
v3?? 2
-
?? 3
)
4.5 Solve: ?? ''
-?? =?? ?? ?? ?? ??
(2018 : 10 Marks)
Solution:
?????????? ?????????? ?????? ???? ?? ''
-?? =?? 2
?? 2??
or (?? 2
-1)?? =?? 2
?? 2??
C.F. : Auxiliary equation is (?? 2
-1)?? =0
???? ?? 2
=1??? =±1
?? ?? =?? 1
?? ?? +?? 2
?? -?? , where ?? 1
and ?? 2
are constants.
?? =
1
?? 2
-1
?? 2
?? 2?? =
1
?? 2
-1
?? 2?? ·?? 2
=?? 2?? 1
(?? +2)
2
-1
·?? 2
=?? 2?? ·
1
?? 2
+4?? +3
·?? 2
=
?? 2?? 3
·
1
1+
?? 2
+4?? 3
·?? 2
=
?? 2?? 3
[1+
?? 2
+4?? 3
]
-1
?? 2
=
?? 2?? 3
[1-
?? 2
3
-
4?? 3
+
(?? 2
+4?? )
2
9
+?.]?? 2
=
?? 2?? 3
[?? 2
-
2
3
-
8?? 3
+
32
9
]
=
?? 2?? 3
[?? 2
-
8?? 3
+
26
3
]
?? =?? ?? +?? ?? =?? 1
?? ?? +?? 2
?? -?? +
?? 2?? 3
[?? 2
-
8?? 3
+
26
9
]
4.6 Solve ?? ''
-?? ?? ''
+????
'
-?? ?? =???? ?? ?? ?? +???? ?? -?? .
(2018: 10 marks)
Solution:
Given equation is ?? ''
-6?? '
+12
'
-8?? -12?? 2?? +27?? -??
or
(?? 3
-6?? 2
+12?? -8)?? =12?? 2?? +27?? -??
C.F. : Auxiliary equation is
?? 3
-6?? 2
+12?? -8=0
? (?? -2)
3
=0
? ?? =2,2,2
? ?? ?? =4?? 2?? +?? 2
?? ?? 2?? +?? 3
?? 2
?? ?? , where ?? 1
,?? 2
,?? 3
are constants.
P.I.: ?? ?? =
1
(?? -2)
3
(12?? 2?? +27?? -?? )
=12×
1
(?? -2)
3
?? 2?? +27×
1
(?? -2)
-
?? -??
=12×
?? 3
3!
?? 2?? +27×
1
(-3)
3
?? -??
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