All questions of Linear Algebra for Electrical Engineering (EE) Exam

If A is a non–singular matrix and the eigen values of A are 2 , 3 , -3 then the eigen values of A-1 are
  • a)
    2 , 3 , - 3
  • b)
    1/2, 1/3, -1/3
  • c)
    2|A|, 3|A|, -3|A|
  • d)
    None of these
Correct answer is option 'B'. Can you explain this answer?

Tanishq Chavan answered
If λ1 ,λ2 ,λ3 ....λare the eigen values of a non–singular matrix A, then A-1 has the eigen values  1/λ1 ,1/λ2 ,1/λ3 ....1/λn Thus eigen values of A-1are 1/2, 1/3, -1/3

The number of linearly independent eigenvectors of 
  • a)
    0    
  • b)
    1    
  • c)
    2    
  • d)
    Infinit e 
Correct answer is 'B'. Can you explain this answer?

Pranjal Sen answered
Number of linear independent vectors is equal to the sum of Geometric Multiplicity of eigen values. Here only eigen value is 2. To find Geometric multiplicity find n-r of (matrix-2I), where n is order and r is rank. Rank of obtained matrix is 1 and n=2 so n-r=1. Therefore the no of linearly independent eigen vectors is 1

The eigenvalues of
  • a)
    -19,5,37
  • b)
    19,-5,-37
  • c)
    2,-3,7
  • d)
    3,-5,37
Correct answer is option 'A'. Can you explain this answer?

Avinash Sharma answered
The eigenvalues of an upper triangular matrix are simply the diagonal entries of the matrix.
Hence 5, -19, and 37 are the eigenvalues of the matrix. Alternately, look atd
λ = 5, -19, 37

If -1 , 2 , 3 are the eigen values of a square matrix A then the eigen values of A2 are
  • a)
    -1 , 2 , 3
  • b)
    1, 4, 9
  • c)
    1, 2, 3
  • d)
    None of these
Correct answer is option 'B'. Can you explain this answer?

Aditya Patel answered
If λ1 ,λ2 ,λ3 ....λare the eigen values of  a matrix A, then A2 has the eigen values  λ12 ,λ22 ,λ32 ....λn2 So, eigen values of Aare 1, 4, 9.

If 1 and 3 are the eigenvalues of a square matrix A then A3 is equal to
  • a)
    13 (A - I2 )
  • b)
    13A - 12 I2
  • c)
    12 (A - I2)
  • d)
    None of these
Correct answer is option 'B'. Can you explain this answer?

Pankaj Rane answered
Since 1 and 3 are the eigenvalues of A so the characteristic equation of A is
Also, by Cayley–Hamilton theorem, every square matrix satisfies its own characteristic equation so

If 2 and 4 are the eigen values of A then the eigenvalues of AT are
  • a)
    1/2, 1/4 
  • b)
    2, 4
  • c)
    4, 16
  • d)
    None of these
Correct answer is option 'B'. Can you explain this answer?

Sanvi Kapoor answered
The eigenvalues of a matrix A are the roots of the characteristic equation of A, which are invariant under the transpose operation. This means that the matrix A and its transpose AT have the same eigenvalues.
Given that 2 and 4 are the eigenvalues of A, the eigenvalues of AT will also be 2 and 4.

Eigen values of a matrix    are 5 and 1. What are the eigen values of the matrix S2  = SS?
  • a)
    1 and 25  
  • b)
    6 and 4  
  • c)
    5 and 1  
  • d)
    2 and 10 
Correct answer is option 'A'. Can you explain this answer?

EduRev GATE answered
We know If λ be the eigen value of A ⇒λ2 is an eigen value of A2 .
For S matrix, if eigen values are λ1, λ2, λ3,... then for S² matrix, the eigen values will be λ²1 λ²2 λ²3......
For S matrix, if eigen values are 1 and 5 then for S² matrix, the eigen values are 1 and 25

In an M × N matrix such that all non-zero entries are covered in a rows and b column. Then the maximum number of non-zero entries, such that no two are on the same row or column, is 
  • a)
    ≤ a + b    
  • b)
    ≤ max (a, b)  
  • c)
    ≤ min[ M –a, N–b]    
  • d)
    ≤ min  {a, b} 
Correct answer is option 'D'. Can you explain this answer?

Naroj Boda answered
Suppose a < b, for example let a = 3, b= 5, then we can put non-zero entries only in 3 rows and 5 columns. So suppose we put non-zero entries in any 3 rows in 3 different columns. Now we can’t put any other non-zero entry anywhere in matrix, because if we put it in some other row, then we will have 4 rows containing non-zeros, if we put it in one of those 3 rows, then we will have more than one non-zero entry in one row, which is not allowed.
So we can fill only “a” non-zero entries if a < b, similarly if b < a, we can put only “b” non-zero entries. So answer is ≤min(a,b), because whatever is less between a and b, we can put atmost that many non-zero entries.

If the rank of a (5×6) matrix Q is 4, then which one of the following statements is correct?  
  • a)
    Q will have four linearly independent rows and four linearly independent columns  
  • b)
    Q will have four lineally independent rows and five lineally independent columns
  • c)
    QQT will be invertible
  • d)
    QTQ will be invertible 
Correct answer is option 'A'. Can you explain this answer?

Given that rank Q is 4, so it will have 4 linearly independent columns as well as 4 linearly independent rows (∵ row rank of a matrix = column rank of a matrix)

So, A is correct and accordingly B is false.

C is false as order of QQ^T will be 5 x 5 and given that rank of Q is 4 i.e. < 5. So the matrix is QQ^T will be singular and hence not invertible.

Similarly D is false as order of Q^T Q will be 6 x 6 and the matrix is Q^T Q will be singular and hence not invertible.

Select a suitable figure from the four alternatives that would complete the figure matrix.

  • a)
     
    1
  • b)
     
    2
  • c)
     
    3
  • d)
    4
Correct answer is option 'D'. Can you explain this answer?

Kiran Datta answered
In each row (as well as each column), the third figure is a combination of all the, elements of the first and the second figures

The eigen values and the corresponding eigen vectors of a 2 × 2 matrix are given by
  • a)
  • b)
  • c)
  • d)
Correct answer is option 'A'. Can you explain this answer?

Harish Thota answered
Actually the trace of matrix is equal to sum of eigen values and det of matrix equal to product of Eigen values. By using the above we can verify and decide the correct answer.

The sum of the eigenvalues of    is equal to 
  • a)
    18
  • b)
    15
  • c)
    10 
  • d)
    none of these
Correct answer is option 'A'. Can you explain this answer?

Zoya Sharma answered
  • Since the sum of the eigenvalues of an n–square matrix is equal to the trace of the matrix (i.e. sum of the diagonal elements)
  • So, required sum = 8 + 5 + 5  = 18

 Find the rank of the matrix 
  • a)
    2
  • b)
  • c)
    0
  • d)
    3
Correct answer is option 'D'. Can you explain this answer?

Engineers Adda answered
To find out the rank of the matrix first find the |A| 
If the value of the |A| = 0 then the matrix is said to be reduced 
But, as the determinant of A has some finite value, then the rank of the matrix is 3.

Find the Eigenvalues of matrix
  • a)
    8, 2
  • b)
    3, -3 
  • c)
    -3, -5 
  • d)
    5, 0
Correct answer is option 'A'. Can you explain this answer?

Zoya Sharma answered
According to the property of the Eigenvalue, the eigenvalues are determined as follows: 
4 + 4 = 8 
3 + 5 = 8 
The sum of the Eigenvalues is equal to the sum of the principal diagonal elements of the matrix.

If 2, - 4 are the eigen values of a non–singular matrix A and |A| = 8, then the eigen values of adjA are:
  • a)
    1/2, -1
  • b)
    2, - 4
  • c)
    2, -1
  • d)
    8, -16
Correct answer is option 'B'. Can you explain this answer?

Starcoders answered
 
  • Eigenvalues of a matrix A are 2 and -4.
  • The determinant ∣A∣ = 8.
  • For a non-singular matrix A, the eigenvalues of adj(A) are given by λ1n−1 and λ2n−1, where n is the order of the matrix.
  • For a 2x2 matrix, the eigenvalues of adj(A) will be 21= 2 and (−4)1= -4.
  • Thus, the eigenvalues of adj(A) are 2 and -4.
Correct answer: b) 2, -4.

For what value of a, if any, will the following system of equations in x, y and z have a solution?  
2x + 3y = 4
x+y+z = 4
x + 2y - z = a
  • a)
    Any real number
  • b)
    0
  • c)
    1
  • d)
    There is no such value
Correct answer is option 'B'. Can you explain this answer?

The correct answer is d.
2x + 3y = 4 ....(1) 
x + y + z = 4 ....(2) 
x + 2y – z = a  ....(3) 

add (2) and (3), 
x + y + z + x + 2y – z =  4 + a 
2x + 3y = 4 + a ....(4) 

from (1) and (4), 
value of a must be 0 otherwise no solution

The lower triangular matrix [L] in the [L][U] decomposition of the matrix given below
is
  • a)
  • b)
  • c)
  • d)
Correct answer is option 'A'. Can you explain this answer?

Vertex Academy answered
We must first complete the first step of forward elimination

First step: Multiply Row 1 by 10/25 = 0.4 and subtract the results from Row 2

Multiply Row 1 by 8/25 = 0.32,  and subtract the results from Row 3
To find ℓ21 and ℓ31 , what multiplier was used to make the a21 and a31 elements zero in the first step of forward elimination using the Naïve Gauss elimination method? They are
21 = 0.4
31 = 0.32
To find ℓ32, what multiplier would be used to make the a32 element zero? Remember the a32 element is made zero in the second step of forward elimination.
So

Hence

If then the value of x is
  • a)
    23/2
  • b)
    13/2
  • c)
    -13/2
  • d)
    -23/2
Correct answer is option 'D'. Can you explain this answer?

Naroj Boda answered

⇒ [(2x - 9)x + 8 x 4x] = 0
⇒ [2x2 - 9x + 32x] = 0
⇒ 2x2 + 23x = 0
⇒ x(2x + 23) = 0
⇒ x = 0 or - 23/2

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