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 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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