Determinants

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New answer posted

a year ago

0 Follower 6 Views

V
Vishal Baghel

Contributor-Level 10

This is a Objective Type Questions as classified in NCERT Exemplar

Sol:

G i v e n     t h a t         | s i n x c o s x c o s x c o s x s i n x c o s x c o s x c o s x s i n x | = 0 C 1 → C 1 + C 2 + C 3 ⇒                                               | 2 c o s x + s i n x c o s x c o s x 2 c o s x + s i n x s i n x c o s x 2 c o s x + s i n x c o s x s i n x | = 0         ( T a k i n g     2 c o s x + s i n x     c o m m o n     f r o m     C 1 ) ⇒                                             ( 2 c o s x + s i n x ) | 1 c o s x c o s x 1 s i n x c o s x 1 c o s x s i n x | = 0 R 1 → R 1 − R 2 , R 2 → R 2 − R 3 ⇒                                                 ( 2 c o s x + s i n x ) | 0 c o s x − s i n x 0 0 s i n x − c o s x c o s x − s i n x 1 c o s x s i n x | = 0 ⇒                                                   ( 2 c o s x + s i n x ) [ 1 | c o s x − s i n x 0 s i n x − c o s x c o s x − s i n x | ] ⇒                                                   ( 2 c o s x + s i n x ) ( c o s x − s i n x ) 2 = 0                   2 c o s x + s i n x = 0                   a n d                   ( c o s x − s i n x ) 2 = 0                                         2 + t a n x = 0                   a n d                         ( c o s x − s i n x ) = 0 ∴                                                   t a n x = − 2             a n d                 ⇒                                     t a n x = 1 B u t           − π 4 ≤ x ≤ π 4                                   a n d                   ⇒                                 t a n x = t a n π 4                                                                                                                                             ∴         x = π 4 ∈ [ − π 4 , π 4 ] S o ,     x &thins

 

New answer posted

a year ago

0 Follower 8 Views

V
Vishal Baghel

Contributor-Level 10

This is a Objective Type Questions as classified in NCERT Exemplar

Sol:

L e t                             Δ = | b 2 − a b b − c b c − a c a b − a 2 a − b b 2 − a b b c − a c c − a a b − a 2 | ⇒                                               = | b ( b − a ) b − c c ( b − a ) a ( b − a ) a − b b ( b − a ) c ( b − a ) c − a a ( b − a ) |         ( T a k i n g     ( b − a )     c o m m o n     f r o m     C 1     a n d     C 3 ) ⇒                                                 = ( b − a ) 2 | b b − c c a a − b b c c − a a | C 1 → C 1 − C 3 ⇒                                                 = ( a − b ) 2 | b − c b − c c a − b a − b b c − a c − a a |     ( C 1     a n d     C 2     a r e     i d e n t i c a l     c o l u m n s . ) ⇒                                                 = ( a − b ) 2 . 0 = 0 H e n c e ,     t h e     c o r r e c t     o p t i o n     i s     ( d ) .

New answer posted

a year ago

0 Follower 21 Views

V
Vishal Baghel

Contributor-Level 10

This is a Objective Type Questions as classified in NCERT Exemplar

Sol:

A r e a     o f     t r i a n g l e     w i t h     v e r t i c e s     ( x 1 , y 1 ) , ( x 2 , y 2 )     a n d     ( x 3 , y 3 )     w i l l     b e :                                                                 Δ = 1 2 | x 1 y 1 1 x 2 y 2 1 x 3 y 3 1 |     ⇒     Δ = 1 2 | − 3 0 1 3 0 1 0 k 1 | ⇒                                                                 = 1 2 [ − 3 | 0 1 k 1 | − 0 | 3 1 0 1 | + 1 | 3 0 0 k | ] ⇒                                                                 = 1 2 [ − 3 ( − k ) − 0 + 1 ( 3 k ) ] ⇒                                                                 = 1 2 ( 3 k + 3 k )     ⇒     = 1 2 ( 6 k ) = 3 k                                                               3 k = 9 ⇒     k = 3 H e n c e ,     t h e     c o r r e c t     o p t i o n     i s     ( b ) .

New answer posted

a year ago

0 Follower 66 Views

V
Vishal Baghel

Contributor-Level 10

This is a Objective Type Questions as classified in NCERT Exemplar

Sol:

H e r e ,     w e     h a v e | a − b b + c a b − a c + a b c − a a + b c | C 2 → C 2 + C 3 ⇒         | a − b a + b + c a b − a a + b + c b c − a a + b + c c | ⇒         ( a + b + c ) | a − b 1 a b − a 1 b c − a 1 c |                             ( T a k i n g     a + b + c     c o m m o n     f r o m     C 2 ) R 1 → R 1 − R 2 ,   R 2 → R 2 − R 3 ⇒         ( a + b + c ) | 2 ( a − b ) 0 a − b b − c 0 b − c c − a 1 c | T a k i n g     ( a − b )     a n d     ( b − c )     c o m m o n     f r o m     R 1     a n d     R 2     r e s p e c t i v e l y ⇒         ( a + b + c ) ( a − b ) ( b − c ) | 2 0 1 1 0 1 c − a 1 c | E x p a n d i n g     a l o n g     C 2 ⇒         ( a + b + c ) ( a − b ) ( b − c ) [ − 1 | 2 1 1 1 | ] ⇒         ( a + b + c ) ( a − b ) ( b − c ) ( − 1 ) ⇒         ( a + b + c ) ( a − b ) ( c − b ) H e n c e ,     t h e     c o r r e c t     x 2     o p t i o n     i s     ( d ) .

New answer posted

a year ago

0 Follower 10 Views

V
Vishal Baghel

Contributor-Level 10

This is a Objective Type Questions as classified in NCERT Exemplar

Sol:

G i v e n     t h a t ⇒                                                   | 2 x 5 8 x | = | 6 − 2 7 3 | ⇒                                                   2 x 2 − 4 0 = 1 8 + 1 4 ⇒ 2 x 2 = 3 2 + 4 0 ⇒                                                                       2 x 2 = 7 2 ⇒ x 2 = 3 6 ∴                                                                                         x ± 6 H e n c e ,     t h e     c o r r e c t     x 2     o p t i o n     i s     ( c ) .

New answer posted

a year ago

0 Follower 7 Views

V
Vishal Baghel

Contributor-Level 10

This is a Short Answer Type Questions as classified in NCERT Exemplar
Sol:

H e r e ,                       A = [ 0 1 1 1 0 1 1 1 0 ]                                           | A | = 0 | 0 1 1 0 | − 1 | 1 1 1 0 | + 1 | 1 0 1 1 |                                                         = 0 − 1 ( 0 − 1 ) + 1 ( 1 − 0 )                                                         = 1 + 1 = 2 ≠ 0     ( non−singular  matrix ) N o w ,     c o − f a c t o r s ,     a 1 1 = + | 0 1 1 0 | = − 1 ,                 a 1 2 = − | 1 1 1 0 | = 1 ,                   a 1 3 = + | 1 0 1 1 | = 1     a 2 1 = − | 1 1 1 0 | = 1 ,                 a 2 2 = + | 0 1 1 0 | = − 1 ,                   a 2 3 = − | 0 1 1 1 | = 1     a 3 1 = + | 1 1 0 1 | = 1 ,                 a 3 2 = − | 0 1 1 1 | = 1 ,                   a 3 3 = + | 0 1 1 0 | = − 1 A d j ( A ) = [ − 1 1 1 1 − 1 1 1 1 − 1 ] ' = [ − 1 1 1 1 − 1 1 1 1 − 1 ] ∴                   A − 1 = 1 | A | A d j ( A ) = 1 2 [ − 1 1 1 1 − 1 1 1 1 − 1 ] N o w ,     A 2 = A . A = [ 0 1 1 1 0 1 1 1 0 ] [ 0 1 1 1 0 1 1 1 0 ]                                           = [ 0 + 1 + 1 0 + 0 + 1 0 + 1 + 0 0 + 0 + 1 1 + 0 + 1 1 + 0 + 0 0 + 1 + 0 1 + 0 + 0 1 + 1 + 0 ] = [ 2 1 1 1 2 1 1 1 2 ] H e n c e ,     A 2 = [ 2 1 1 1 2 1 1 1 2 ] N o w ,     w e     h a v e     t o     p r o v e     t h a t     A − 1 = A 2 − 3 I 2 R . H . S . = [ 2 1 1 1 2 1 1 1 2 ] − 3 [ 1 0 0 0 1 0 0 0 1 ] 2                                 = [ 2 1 1 1 2 1 1 1 2 ] − [ 3 0 0 0 3 0 0 0 3 ] 2 = 1 2 [ − 1 1 1 1 − 1 1 1 1 − 1 ]                                   = A − 1 = L . H . S . H e n c e ,     p r o v e d .

New answer posted

a year ago

0 Follower 7 Views

V
Vishal Baghel

Contributor-Level 10

This is a Short Answer Type Questions as classified in NCERT Exemplar
Sol:

| 1 1 1 1 + c o s A 1 + c o s B 1 + c o s C c o s 2 A + c o s A c o s 2 B + c o s B c o s 2 C + c o s C | = 0 C 1 → C 1 − C 2 ,   C 2 → C 2 − C 3 ⇒         | 0 0 1 c o s A − c o s B c o s B − c o s C 1 + c o s C c o s 2 A + c o s A − c o s 2 B − c o s B c o s 2 B + c o s B − c o s 2 C − c o s C c o s 2 C + c o s C | = 0 ⇒         | 0 0 1 c o s A − c o s B c o s B − c o s C 1 + c o s C c o s 2 A − c o s 2 B + c o s A − c o s B c o s 2 B − c o s 2 C + c o s B − c o s C c o s 2 C + c o s C | = 0 ⇒         | 0 0 1 c o s A − c o s B c o s B − c o s C 1 + c o s C ( c o s A + c o s B ) * ( c o s A − c o s B ) + ( c o s A − c o s B ) ( c o s B + c o s C ) * ( c o s B − c o s C ) + c o s B − c o s C c o s 2 C + c o s C | = 0 T a k i n g     ( c o s A − c o s B )     a n d     ( c o s B − c o s C )     c o m m o n     f r o m     C 1     a n d     C 2     r e s p e c t i v e l y . ⇒ ( c o s A − c o s B ) ( c o s B − c o s C ) | 0 0 1 1 1 1 + c o s C c o s A + c o s B + 1 c o s B + c o s C + 1 c o s 2 C + c o s C | = 0 E x p a n d i n g     a l o n g     R 1 ⇒ ( c o s A − c o s B ) ( c o s B − c o s C ) [ 1 | 1 1 c o s A + c o s B + 1 c o s B + c o s C + 1 | ] = 0 ⇒ ( c o s A − c o s B ) ( c o s B − c o s C ) [ ( c o s B + c o s C + 1 ) − ( c o s A + c o s B + 1 ) ] = 0 ⇒ ( c o s A − c o s B ) ( c o s B − c o s C ) [ c o s B + c o s C + 1 − c o s A − c o s B − 1 ] = 0 ⇒ ( c o s A − c o s B ) ( c o s B − c o s C ) ( c o s C − c o s A ) = 0 ⇒ c o s A − c o s B = 0         o r         c o s B − c o s C = 0         o r         c o s C − c o s A = 0 ⇒ c o s A = c o s B         o r         c o s B = c o s C         o r         c o s C = c o s A ⇒ ∠ A = ∠ C         o r         ∠ B = ∠ C         ⇒         ∠ A = ∠ B H e n c e ,     Δ A B C     i s     a n     i s o s c e l e s     t r i a n g l e .

New answer posted

a year ago

0 Follower 12 Views

V
Vishal Baghel

Contributor-Level 10

This is a Short Answer Type Questions as classified in NCERT Exemplar
Sol:

If  the  given  points  lie  on  a  straight  line,  then  the  area  of  the  triangle  formed  by  joining  the points  pairwise  is  zero. S 0 ,           | a + 5 a − 4 1 a − 2 a + 3 1 a a 1 | R 1 → R 1 − R 2 ,   R 2 → R 2 − R 3 ⇒                                                       | 7 − 7 0 − 2 3 0 a a 1 | E x p a n d i n g     a l o n g     C 3 ⇒                                                         1 . | 7 − 7 − 2 3 | = 2 1 − 1 4 = 7 u n i t s As  7≠0.  Hence,  the  three  points  do  not  lie  on  a  straight  line  for  any  value  of  a.

New answer posted

a year ago

0 Follower 10 Views

V
Vishal Baghel

Contributor-Level 10

This is a Short Answer Type Questions as classified in NCERT Exemplar
Sol:

I f     a 1 , a 2 , a 3 , … a r     b e     t h e     t e r m s     o f     G . P . ,     t h e n                                                                                       a n = A R n − 1 ( w h e r e     A     i s     t h e     f i r s t     t e r m     a n d     R     i s     t h e     c o m m o n     r a t i o     o f     t h e     G . P . ) ∴               a r + 1 = A R r + 1 − 1 = A R r ;     a r + 5 = A R r + 5 − 1 = A R r + 4                     a r + 9 = A R r + 9 − 1 = A R r + 8 ;     a r + 7 = A R r + 7 − 1 = A R r + 6                     a r + 1 1 = A R r + 1 1 − 1 = A R r + 1 0 ;     a r + 1 5 = A R r + 1 5 − 1 = A R r + 1 4                     a r + 1 7 = A R r + 1 7 − 1 = A R r + 1 6 ;     a r + 2 1 = A R r + 2 1 − 1 = A R r + 2 0 ∴  The  determinant  becomes                                                                       | A R r A R r + 4 A R r + 8 A R r + 6 A R r + 1 0 A R r + 1 4 A R r + 1 0 A R r + 1 6 A R r + 2 0 | T a k i n g     A R r ,   A R r + 6     a n d     A R r + 1 0     c o m m o n     f r o m     R 1 ,   R 2 ,       a n d     R 3       r e s p e c t i v e l y .                                                                       A R r . A R r + 6 . A R r + 1 0 | 1 R 4 R 8 1 R 4 R 8 1 R 6 R 1 0 |                                                                     = A R r . A R r + 6 . A R r + 1 0 | 0 |                   [ ?     R 1       a n d     R 2       a r e     i d e n t i c a l     r o w s ]                                                                     = 0 Hence,  the  given  determinant  is  independent  of  r.

New answer posted

a year ago

0 Follower 5 Views

V
Vishal Baghel

Contributor-Level 10

This is a Short Answer Type Questions as classified in NCERT Exemplar
Sol:

L e t                             A = [ 4 − x 4 + x 4 + x 4 + x 4 − x 4 + x 4 + x 4 + x 4 − x ] = 0                                         | A | = | 4 − x 4 + x 4 + x 4 + x 4 − x 4 + x 4 + x 4 + x 4 − x | = 0 R 1 → R 1 + R 2 + R 3 ⇒                                                       | 1 2 + x 1 2 + x 1 2 + x 4 + x 4 − x 4 + x 4 + x 4 + x 4 − x | = 0 T a k i n g     ( 1 2 + x ) c o m m o n     f r o m     R 1 ⇒                                                       ( 1 2 + x ) | 1 1 1 4 + x 4 − x 4 + x 4 + x 4 + x 4 − x | = 0 C 1 → C 1 − C 2 , C 2 → C 2 − C 3 ⇒                                                       ( 1 2 + x ) | 0 0 1 2 x − 2 x 4 + x 0 2 x 4 − x | = 0 E x p a n d i n g     a l o n g     R 1 ⇒                                                         ( 1 2 + x ) [ 1 . | 2 x − 2 x 0 2 x | ] = 0 ⇒                                                         ( 1 2 + x ) ( 4 x 2 − 0 ) = 0 ⇒ 1 2 + x = 0     o r     4 x 2 = 0 ⇒                                                         x = − 1 2         o r         x = 0

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