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 Page 1


Edurev123 
3 Matrix 
3.1 Find a hermitian and a skew-hermitian matrix each whose sum is the matrix 
[
?? ?? ?? -?? ?? ?? +?? ?? ?? -?? +?? ?? ?? ?? ] 
(2009 : 12 Marks) 
Solution: 
Given any matrix ?? we can write it as 
?? =
1
2
(?? +?? ?
)+
1
2
(?? -?? *
) 
where ?? *
 is the complex tranjugate of ?? . Also 
1
2
(?? +?? *
) is always hermitian as 
[
1
2
(?? +?? *
)]
*
 =
1
2
(?? +?? *
)
*
=
1
2
(?? *
+?? )
 =
1
2
(?? +?? *
)
 
And 
1
2
(?? +?? *
) is skew hermitian as 
                        [
1
2
(?? -?? *
)]* =
1
2
(?? *
-?? )=-[
1
2
(?? -?? *
)]
? ?? =
1
2
[?? +?? *
]+
1
2
[?? -?? *
]
=?? +?? 
where ?? is hermitian and ?? skew hermitian. 
Taking ?? as given matrix. 
?? =
1
2
(?? +?? *
)
 =
1
2
{[
2?? 3 -1
1 2+3?? 2
-?? +1 4 5?? ]+[
-2?? ?? ?? +1
3 2-3?? 4
-1 2 -5?? ]}
 =[
0 2 ??/2
2 2 3
-??/2 3 0
] which is hermitian. 
 
??????                               ?? =
1
2
(?? -?? *
) 
Page 2


Edurev123 
3 Matrix 
3.1 Find a hermitian and a skew-hermitian matrix each whose sum is the matrix 
[
?? ?? ?? -?? ?? ?? +?? ?? ?? -?? +?? ?? ?? ?? ] 
(2009 : 12 Marks) 
Solution: 
Given any matrix ?? we can write it as 
?? =
1
2
(?? +?? ?
)+
1
2
(?? -?? *
) 
where ?? *
 is the complex tranjugate of ?? . Also 
1
2
(?? +?? *
) is always hermitian as 
[
1
2
(?? +?? *
)]
*
 =
1
2
(?? +?? *
)
*
=
1
2
(?? *
+?? )
 =
1
2
(?? +?? *
)
 
And 
1
2
(?? +?? *
) is skew hermitian as 
                        [
1
2
(?? -?? *
)]* =
1
2
(?? *
-?? )=-[
1
2
(?? -?? *
)]
? ?? =
1
2
[?? +?? *
]+
1
2
[?? -?? *
]
=?? +?? 
where ?? is hermitian and ?? skew hermitian. 
Taking ?? as given matrix. 
?? =
1
2
(?? +?? *
)
 =
1
2
{[
2?? 3 -1
1 2+3?? 2
-?? +1 4 5?? ]+[
-2?? ?? ?? +1
3 2-3?? 4
-1 2 -5?? ]}
 =[
0 2 ??/2
2 2 3
-??/2 3 0
] which is hermitian. 
 
??????                               ?? =
1
2
(?? -?? *
) 
 =
1
2
{[
2?? 3 -1
1 2+3?? 2
-?? +1 4 5?? ]-[
-2?? ?? ?? +1
3 2-3?? 4
-1 2 -5?? ]}
 =
[
 
 
 
 2?? 1
-(?? +2)
2
-1 3?? -1
(-?? +2)
2
1 5?? ]
 
 
 
  
So, ?? and ?? are required vector where 
?? =?? +?? 
and ?? is Hermitian and ?? skew Hermitian. 
3.2 Find a ?? ×?? real matrix ?? which is both orthogonal and skew symmetric. Can 
there exist a ?? ×?? real matrix which is both orthogonal and skaw symmetric. 
Justify your answer. 
(2009 : 20 Marks) 
Solution: 
Approach : Consider the form of a skew symmetric matrix (diagonal elements zero) and 
impose conditions for orthogonality. 
Let ?? be a 2×2 skew symmetric matrix and ?? =[
?? ?? ?? ?? ]. 
?? is skew symmetric ?                                ?? =-?? ??  
=>                                                           [
?? ?? ?? ?? ]=[
-?? -?? -?? -?? ]??? =?? 
=0 and ?? =-?? 
?                                                                          ?? =[
0 ?? -?? 0
] 
If ?? is orthogonal then ?? ?? ?
=?? 
=>                                                                  ?? 2
=1??? =±?? 
?[
0 1
-1 0
] and [
0 -1
1 0
] are the only matrices that are orthogonal and skew symmetric. 
Again let ?? be a 3×3 skew symmetric matrix. Then 
?? =[
0 ?? ?? -?? 0 ?? -?? -?? 0
] as seen in previous case.  
Also if ?? is orthogonal. 
Page 3


Edurev123 
3 Matrix 
3.1 Find a hermitian and a skew-hermitian matrix each whose sum is the matrix 
[
?? ?? ?? -?? ?? ?? +?? ?? ?? -?? +?? ?? ?? ?? ] 
(2009 : 12 Marks) 
Solution: 
Given any matrix ?? we can write it as 
?? =
1
2
(?? +?? ?
)+
1
2
(?? -?? *
) 
where ?? *
 is the complex tranjugate of ?? . Also 
1
2
(?? +?? *
) is always hermitian as 
[
1
2
(?? +?? *
)]
*
 =
1
2
(?? +?? *
)
*
=
1
2
(?? *
+?? )
 =
1
2
(?? +?? *
)
 
And 
1
2
(?? +?? *
) is skew hermitian as 
                        [
1
2
(?? -?? *
)]* =
1
2
(?? *
-?? )=-[
1
2
(?? -?? *
)]
? ?? =
1
2
[?? +?? *
]+
1
2
[?? -?? *
]
=?? +?? 
where ?? is hermitian and ?? skew hermitian. 
Taking ?? as given matrix. 
?? =
1
2
(?? +?? *
)
 =
1
2
{[
2?? 3 -1
1 2+3?? 2
-?? +1 4 5?? ]+[
-2?? ?? ?? +1
3 2-3?? 4
-1 2 -5?? ]}
 =[
0 2 ??/2
2 2 3
-??/2 3 0
] which is hermitian. 
 
??????                               ?? =
1
2
(?? -?? *
) 
 =
1
2
{[
2?? 3 -1
1 2+3?? 2
-?? +1 4 5?? ]-[
-2?? ?? ?? +1
3 2-3?? 4
-1 2 -5?? ]}
 =
[
 
 
 
 2?? 1
-(?? +2)
2
-1 3?? -1
(-?? +2)
2
1 5?? ]
 
 
 
  
So, ?? and ?? are required vector where 
?? =?? +?? 
and ?? is Hermitian and ?? skew Hermitian. 
3.2 Find a ?? ×?? real matrix ?? which is both orthogonal and skew symmetric. Can 
there exist a ?? ×?? real matrix which is both orthogonal and skaw symmetric. 
Justify your answer. 
(2009 : 20 Marks) 
Solution: 
Approach : Consider the form of a skew symmetric matrix (diagonal elements zero) and 
impose conditions for orthogonality. 
Let ?? be a 2×2 skew symmetric matrix and ?? =[
?? ?? ?? ?? ]. 
?? is skew symmetric ?                                ?? =-?? ??  
=>                                                           [
?? ?? ?? ?? ]=[
-?? -?? -?? -?? ]??? =?? 
=0 and ?? =-?? 
?                                                                          ?? =[
0 ?? -?? 0
] 
If ?? is orthogonal then ?? ?? ?
=?? 
=>                                                                  ?? 2
=1??? =±?? 
?[
0 1
-1 0
] and [
0 -1
1 0
] are the only matrices that are orthogonal and skew symmetric. 
Again let ?? be a 3×3 skew symmetric matrix. Then 
?? =[
0 ?? ?? -?? 0 ?? -?? -?? 0
] as seen in previous case.  
Also if ?? is orthogonal. 
? ????
?
=?? ? [
0 ?? ?? -?? 0 ?? -?? -?? 0
][
0 -?? -?? ?? 0 -?? ?? ?? 0
] =[
1 0 0
0 1 0
0 0 1
]
? [
?? 2
+?? 2
???? -????
???? ?? 2
+?? 2
????
-???? ???? ?? 2
-?? 2
] =[
1 0 0
0 1 0
0 0 1
]
? ?? 2
+?? 2
=?? 2
+?? 2
=?? 2
+?? 2
=1                  …(i)
=???? =???? =???? =0                                           …(ii)
 
From (ii) two of ?? ,?? ,?? must be zero if ?? =?? =0??? 2
+?? 2
=0?1. 
Similarly in other cases it can be shown the system of equations is not compatible. 
So, a 3×3 skew symmetric matrix can not be orthogonal. 
 
3.3. If ?? ?? ,?? ?? ,?? ?? are eigen values of the matrix 
?? =[
?? ?? -?? ?? ?? ???? ?? ?? ?? ????
] 
Show that v?? ?? ?? +?? ?? ?? +?? ?? ?? =v???????? 
(2010 : 12 Marks) 
 
Solution: 
?????????? ?? h?? ????????????                                       ?? =[
26 -2 2
2 21 4
4 2 28
] 
Now, finding eigen values of ?? 
Page 4


Edurev123 
3 Matrix 
3.1 Find a hermitian and a skew-hermitian matrix each whose sum is the matrix 
[
?? ?? ?? -?? ?? ?? +?? ?? ?? -?? +?? ?? ?? ?? ] 
(2009 : 12 Marks) 
Solution: 
Given any matrix ?? we can write it as 
?? =
1
2
(?? +?? ?
)+
1
2
(?? -?? *
) 
where ?? *
 is the complex tranjugate of ?? . Also 
1
2
(?? +?? *
) is always hermitian as 
[
1
2
(?? +?? *
)]
*
 =
1
2
(?? +?? *
)
*
=
1
2
(?? *
+?? )
 =
1
2
(?? +?? *
)
 
And 
1
2
(?? +?? *
) is skew hermitian as 
                        [
1
2
(?? -?? *
)]* =
1
2
(?? *
-?? )=-[
1
2
(?? -?? *
)]
? ?? =
1
2
[?? +?? *
]+
1
2
[?? -?? *
]
=?? +?? 
where ?? is hermitian and ?? skew hermitian. 
Taking ?? as given matrix. 
?? =
1
2
(?? +?? *
)
 =
1
2
{[
2?? 3 -1
1 2+3?? 2
-?? +1 4 5?? ]+[
-2?? ?? ?? +1
3 2-3?? 4
-1 2 -5?? ]}
 =[
0 2 ??/2
2 2 3
-??/2 3 0
] which is hermitian. 
 
??????                               ?? =
1
2
(?? -?? *
) 
 =
1
2
{[
2?? 3 -1
1 2+3?? 2
-?? +1 4 5?? ]-[
-2?? ?? ?? +1
3 2-3?? 4
-1 2 -5?? ]}
 =
[
 
 
 
 2?? 1
-(?? +2)
2
-1 3?? -1
(-?? +2)
2
1 5?? ]
 
 
 
  
So, ?? and ?? are required vector where 
?? =?? +?? 
and ?? is Hermitian and ?? skew Hermitian. 
3.2 Find a ?? ×?? real matrix ?? which is both orthogonal and skew symmetric. Can 
there exist a ?? ×?? real matrix which is both orthogonal and skaw symmetric. 
Justify your answer. 
(2009 : 20 Marks) 
Solution: 
Approach : Consider the form of a skew symmetric matrix (diagonal elements zero) and 
impose conditions for orthogonality. 
Let ?? be a 2×2 skew symmetric matrix and ?? =[
?? ?? ?? ?? ]. 
?? is skew symmetric ?                                ?? =-?? ??  
=>                                                           [
?? ?? ?? ?? ]=[
-?? -?? -?? -?? ]??? =?? 
=0 and ?? =-?? 
?                                                                          ?? =[
0 ?? -?? 0
] 
If ?? is orthogonal then ?? ?? ?
=?? 
=>                                                                  ?? 2
=1??? =±?? 
?[
0 1
-1 0
] and [
0 -1
1 0
] are the only matrices that are orthogonal and skew symmetric. 
Again let ?? be a 3×3 skew symmetric matrix. Then 
?? =[
0 ?? ?? -?? 0 ?? -?? -?? 0
] as seen in previous case.  
Also if ?? is orthogonal. 
? ????
?
=?? ? [
0 ?? ?? -?? 0 ?? -?? -?? 0
][
0 -?? -?? ?? 0 -?? ?? ?? 0
] =[
1 0 0
0 1 0
0 0 1
]
? [
?? 2
+?? 2
???? -????
???? ?? 2
+?? 2
????
-???? ???? ?? 2
-?? 2
] =[
1 0 0
0 1 0
0 0 1
]
? ?? 2
+?? 2
=?? 2
+?? 2
=?? 2
+?? 2
=1                  …(i)
=???? =???? =???? =0                                           …(ii)
 
From (ii) two of ?? ,?? ,?? must be zero if ?? =?? =0??? 2
+?? 2
=0?1. 
Similarly in other cases it can be shown the system of equations is not compatible. 
So, a 3×3 skew symmetric matrix can not be orthogonal. 
 
3.3. If ?? ?? ,?? ?? ,?? ?? are eigen values of the matrix 
?? =[
?? ?? -?? ?? ?? ???? ?? ?? ?? ????
] 
Show that v?? ?? ?? +?? ?? ?? +?? ?? ?? =v???????? 
(2010 : 12 Marks) 
 
Solution: 
?????????? ?? h?? ????????????                                       ?? =[
26 -2 2
2 21 4
4 2 28
] 
Now, finding eigen values of ?? 
      [
26-?? -2 2
2 21-?? 4
4 2 28-?? ]=0
  ?                   (26-?? )[(21-?? )(28-?? )-8]+2[56-2?? -16]+2[4-84+4?? )=0
   ?                                         (26-?? )[588-49?? +?? 2
-8]+2[40-2?? ]+2[4?? -80]=0
  ?                                                          (26-?? )[580-49?? +?? 2
]+80-4?? +8?? -160=0
  ?                                              15080-1274?? +26?? 2
-580?? +49?? 2
-?? 3
-80+4?? =0
  ?                                                                                                 15000-1850?? +75?? 2
-?? 3
=0
  ?                                                                                                   ?? 3
-75?? 2
+??850?? -??5000=0
  ?????? ?? 1
,?? 2
,?? 3
 ???? ?????????? ???? ???? .(1) 
  ?                                                                  ?? 1
+?? 2
+?? 3
=75
                                                           ?? 1
?? 2
+?? 2
?? 3
+?? 3
?? 4
=1850
                                                                                   ?? 1
?? 2
?? 3
=15000
 ???????? ,                                                       (?? 1
+?? 2
+?? 3
)
2
=?? 2
1
+?? 2
2
+?? 3
2
+2(?? 1
?? 2
+?? 2
?? 3
+?? 3
?? 1
)
 
Putting above values in above eqn., we get 
(75)
2
=?? 1
2
+?? 2
2
+?? 3
2
+2(1850) 
?                                       ?? 1
2
+?? 2
2
+?? 3
2
=5625-3700 
 ?                                     ?? 1
2
+?? 2
2
+?? 3
2
=1925=1949
 ?                                     v?? 1
2
+?? 2
2
+?? 3
2
=v1949
 
3.4 Let ?? and ?? be ?? ×?? matrices over reals. Show that ?? -???? is invertible if ?? -
???? is invertible. Deduce that ???? and ???? have same eigen values. 
(2010 : 20 Marks) 
Solution: 
Given ?? and ?? are two ?? ×?? matrices over reels. 
 Let                                                      ?? =(?? -???? )
-1
                                             (Assuming that ?? -AB is invertible) 
 ?                                                        ?? =?? +???? +(???? )
2
+(???? )
3
+?..                        (By binomial expansion) 
?????? ,                                           ?? ×?? =???? +(???? )
2
+(???? )
3
+?
 ?                                         ?? ×?? ×?? =?? +???? +(???? )
2
+(???? )
3
+?
                                                                 =(?? -???? )
-1
 
?(?? -???? ) is invertible if ?? -???? is invertible. 
To show that ???? and ???? have same eigen values. Let ?? be an eigen-value of ???? , 
Case 1 : if ?? =0, then                            ?????? =0.??                                           (?? -
?????????? ???????????? ) 
=>                                                  (0.?? -???? )?? =0 
Page 5


Edurev123 
3 Matrix 
3.1 Find a hermitian and a skew-hermitian matrix each whose sum is the matrix 
[
?? ?? ?? -?? ?? ?? +?? ?? ?? -?? +?? ?? ?? ?? ] 
(2009 : 12 Marks) 
Solution: 
Given any matrix ?? we can write it as 
?? =
1
2
(?? +?? ?
)+
1
2
(?? -?? *
) 
where ?? *
 is the complex tranjugate of ?? . Also 
1
2
(?? +?? *
) is always hermitian as 
[
1
2
(?? +?? *
)]
*
 =
1
2
(?? +?? *
)
*
=
1
2
(?? *
+?? )
 =
1
2
(?? +?? *
)
 
And 
1
2
(?? +?? *
) is skew hermitian as 
                        [
1
2
(?? -?? *
)]* =
1
2
(?? *
-?? )=-[
1
2
(?? -?? *
)]
? ?? =
1
2
[?? +?? *
]+
1
2
[?? -?? *
]
=?? +?? 
where ?? is hermitian and ?? skew hermitian. 
Taking ?? as given matrix. 
?? =
1
2
(?? +?? *
)
 =
1
2
{[
2?? 3 -1
1 2+3?? 2
-?? +1 4 5?? ]+[
-2?? ?? ?? +1
3 2-3?? 4
-1 2 -5?? ]}
 =[
0 2 ??/2
2 2 3
-??/2 3 0
] which is hermitian. 
 
??????                               ?? =
1
2
(?? -?? *
) 
 =
1
2
{[
2?? 3 -1
1 2+3?? 2
-?? +1 4 5?? ]-[
-2?? ?? ?? +1
3 2-3?? 4
-1 2 -5?? ]}
 =
[
 
 
 
 2?? 1
-(?? +2)
2
-1 3?? -1
(-?? +2)
2
1 5?? ]
 
 
 
  
So, ?? and ?? are required vector where 
?? =?? +?? 
and ?? is Hermitian and ?? skew Hermitian. 
3.2 Find a ?? ×?? real matrix ?? which is both orthogonal and skew symmetric. Can 
there exist a ?? ×?? real matrix which is both orthogonal and skaw symmetric. 
Justify your answer. 
(2009 : 20 Marks) 
Solution: 
Approach : Consider the form of a skew symmetric matrix (diagonal elements zero) and 
impose conditions for orthogonality. 
Let ?? be a 2×2 skew symmetric matrix and ?? =[
?? ?? ?? ?? ]. 
?? is skew symmetric ?                                ?? =-?? ??  
=>                                                           [
?? ?? ?? ?? ]=[
-?? -?? -?? -?? ]??? =?? 
=0 and ?? =-?? 
?                                                                          ?? =[
0 ?? -?? 0
] 
If ?? is orthogonal then ?? ?? ?
=?? 
=>                                                                  ?? 2
=1??? =±?? 
?[
0 1
-1 0
] and [
0 -1
1 0
] are the only matrices that are orthogonal and skew symmetric. 
Again let ?? be a 3×3 skew symmetric matrix. Then 
?? =[
0 ?? ?? -?? 0 ?? -?? -?? 0
] as seen in previous case.  
Also if ?? is orthogonal. 
? ????
?
=?? ? [
0 ?? ?? -?? 0 ?? -?? -?? 0
][
0 -?? -?? ?? 0 -?? ?? ?? 0
] =[
1 0 0
0 1 0
0 0 1
]
? [
?? 2
+?? 2
???? -????
???? ?? 2
+?? 2
????
-???? ???? ?? 2
-?? 2
] =[
1 0 0
0 1 0
0 0 1
]
? ?? 2
+?? 2
=?? 2
+?? 2
=?? 2
+?? 2
=1                  …(i)
=???? =???? =???? =0                                           …(ii)
 
From (ii) two of ?? ,?? ,?? must be zero if ?? =?? =0??? 2
+?? 2
=0?1. 
Similarly in other cases it can be shown the system of equations is not compatible. 
So, a 3×3 skew symmetric matrix can not be orthogonal. 
 
3.3. If ?? ?? ,?? ?? ,?? ?? are eigen values of the matrix 
?? =[
?? ?? -?? ?? ?? ???? ?? ?? ?? ????
] 
Show that v?? ?? ?? +?? ?? ?? +?? ?? ?? =v???????? 
(2010 : 12 Marks) 
 
Solution: 
?????????? ?? h?? ????????????                                       ?? =[
26 -2 2
2 21 4
4 2 28
] 
Now, finding eigen values of ?? 
      [
26-?? -2 2
2 21-?? 4
4 2 28-?? ]=0
  ?                   (26-?? )[(21-?? )(28-?? )-8]+2[56-2?? -16]+2[4-84+4?? )=0
   ?                                         (26-?? )[588-49?? +?? 2
-8]+2[40-2?? ]+2[4?? -80]=0
  ?                                                          (26-?? )[580-49?? +?? 2
]+80-4?? +8?? -160=0
  ?                                              15080-1274?? +26?? 2
-580?? +49?? 2
-?? 3
-80+4?? =0
  ?                                                                                                 15000-1850?? +75?? 2
-?? 3
=0
  ?                                                                                                   ?? 3
-75?? 2
+??850?? -??5000=0
  ?????? ?? 1
,?? 2
,?? 3
 ???? ?????????? ???? ???? .(1) 
  ?                                                                  ?? 1
+?? 2
+?? 3
=75
                                                           ?? 1
?? 2
+?? 2
?? 3
+?? 3
?? 4
=1850
                                                                                   ?? 1
?? 2
?? 3
=15000
 ???????? ,                                                       (?? 1
+?? 2
+?? 3
)
2
=?? 2
1
+?? 2
2
+?? 3
2
+2(?? 1
?? 2
+?? 2
?? 3
+?? 3
?? 1
)
 
Putting above values in above eqn., we get 
(75)
2
=?? 1
2
+?? 2
2
+?? 3
2
+2(1850) 
?                                       ?? 1
2
+?? 2
2
+?? 3
2
=5625-3700 
 ?                                     ?? 1
2
+?? 2
2
+?? 3
2
=1925=1949
 ?                                     v?? 1
2
+?? 2
2
+?? 3
2
=v1949
 
3.4 Let ?? and ?? be ?? ×?? matrices over reals. Show that ?? -???? is invertible if ?? -
???? is invertible. Deduce that ???? and ???? have same eigen values. 
(2010 : 20 Marks) 
Solution: 
Given ?? and ?? are two ?? ×?? matrices over reels. 
 Let                                                      ?? =(?? -???? )
-1
                                             (Assuming that ?? -AB is invertible) 
 ?                                                        ?? =?? +???? +(???? )
2
+(???? )
3
+?..                        (By binomial expansion) 
?????? ,                                           ?? ×?? =???? +(???? )
2
+(???? )
3
+?
 ?                                         ?? ×?? ×?? =?? +???? +(???? )
2
+(???? )
3
+?
                                                                 =(?? -???? )
-1
 
?(?? -???? ) is invertible if ?? -???? is invertible. 
To show that ???? and ???? have same eigen values. Let ?? be an eigen-value of ???? , 
Case 1 : if ?? =0, then                            ?????? =0.??                                           (?? -
?????????? ???????????? ) 
=>                                                  (0.?? -???? )?? =0 
?                                         (0.?? -???? )?? =0
? 0 =|0.?? -???? |=|-?? ||?? |=|?? ||-?? |
=|0.?? -???? |
 
?0 is an eigen-value of ???? aiso. 
Case 2 : If ?? ?0. Let ?? is not an eigen-value of ???? . Then 
?????? ????? ?(???? -???? )?? ?0
? |???? -???? |?0??? ?? |
1
?? ???? -1| ?0
 ? |
????
?? -?? |?0?|
?? ?? ·?? -?? |?0
 or 
|?? -
?? ?? ·?? |?0??? -
?? ?? ·?? is invertihle. 
 
? By abc e deduction, it can be concluded that ?? -?? ·
?? ?? is also invertible. 
? |?? -?? ·
?? ?? |?0
? ?? ?? |?? -
?? -?? ?? |?0
? |???? -???? |?0
 
??? is not an eigen-value of ???? which contradicts our assumption. 
??? is an eigen-value of ???? also. 
????? and ???? have same eigen-values. 
3.5 Let ?? be a non-singular, ?? ×?? square matrix. Show that ?? ( adj. ?? )=|?? |.?? ?? . 
Hence, show that ladj. (Adj. ?? )|=|?? |
(?? -?? )
?? . 
(2011: 10 Marks) 
Solution: 
If ?? be any ?? -rowed square matrix, then 
(adj.?? )?? =?? (adj.?? )=|?? |?? ?? (??) 
where ?? ?? is a unit matrix of order ?? and adj. ?? is adjoint of the matrix ?? . 
Replacing ?? by adj. ?? in (i), we get 
                                        ( adj. A)(adj. adj. A) =|adj.A|?? ?? 
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FAQs on Matrix - Mathematics Optional Notes for UPSC

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Ans. Candidates must be a citizen of India, hold a bachelor's degree from a recognized university, and meet the age limit criteria to be eligible for the UPSC exam. The age limit varies depending on the category of the candidate.
4. How many stages are there in the UPSC exam?
Ans. The UPSC exam consists of three stages - Preliminary Examination (Objective Type), Main Examination (Written), and Personality Test (Interview).
5. Can I choose the language for the UPSC exam?
Ans. Yes, candidates can choose to write the UPSC exam in any of the scheduled languages mentioned in the Eighth Schedule of the Constitution or in English.
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