Linear-Algebra
Question 1 |
I. X is invertible.
II. Determinant of X is non-zero.
Which one of the following is TRUE?
I implies II; II does not imply I. | |
II implies I; I does not imply II. | |
I and II are equivalent statements. | |
I does not imply II; II does not imply I. |
That means we can also say that determinant of X is non-zero.
Question 2 |
Consider the following matrix:

The absolute value of the product of Eigen values of R is ______.
12 | |
17 | |
10 | |
8 |

Question 3 |

The largest eigenvalue of A is ________
3 | |
4 | |
5 | |
6 |

→ Correction in Explanation:

⇒ (1 - λ)(2 - λ) - 2 = 0
⇒ λ2 - 3λ=0
λ = 0, 3
So maximum is 3.
Question 4 |
Assume that multiplying a matrix G1 of dimension p×q with another matrix G2 of dimension q×r requires pqr scalar multiplications. Computing the product of n matrices G1G2G3…Gn can be done by parenthesizing in different ways. Define GiGi+1 as an explicitly computed pair for a given parenthesization if they are directly multiplied. For example, in the matrix multiplication chain G1G2G3G4G5G6 using parenthesization(G1(G2G3))(G4(G5G6)), G2G3 and G5G6 are the only explicitly computed pairs.
Consider a matrix multiplication chain F1F2F3F4F5, where matrices F1, F2, F3, F4 and F5 are of dimensions 2×25, 25×3, 3×16, 16×1 and 1×1000, respectively. In the parenthesization of F1F2F3F4F5 that minimizes the total number of scalar multiplications, the explicitly computed pairs is/ are
F1F2 and F3F4 only
| |
F2F3 only | |
F3F4 only | |
F1F2 and F4F5 only
|
→ Optimal Parenthesization is:
((F1(F2(F3 F4)))F5)
→ But according to the problem statement we are only considering F3, F4 explicitly computed pairs.
Question 5 |
Consider Guwahati (G) and Delhi (D) whose temperatures can be classified as high (H), medium (M) and low (L). Let P(HG) denote the probability that Guwahati has high temperature. Similarly, P(MG) and P(LG) denotes the probability of Guwahati having medium and low temperatures respectively. Similarly, we use P(HD), P(MD) and P(LD) for Delhi.
The following table gives the conditional probabilities for Delhi’s temperature given Guwahati’s temperature.

Consider the first row in the table above. The first entry denotes that if Guwahati has high temperature (HG) then the probability of Delhi also having a high temperature (HD) is 0.40; i.e., P(HD ∣ HG) = 0.40. Similarly, the next two entries are P(MD ∣ HG) = 0.48 and P(LD ∣ HG) = 0.12. Similarly for the other rows.
If it is known that P(HG) = 0.2, P(MG) = 0.5, and P(LG) = 0.3, then the probability (correct to two decimal places) that Guwahati has high temperature given that Delhi has high temperature is _______ .
0.60 | |
0.61 | |
0.62 | |
0.63 |

The first entry denotes that if Guwahati has high temperature (HG ) then the probability that Delhi also having a high temperature (HD ) is 0.40.
P (HD / HG ) = 0.40
We need to find out the probability that Guwahati has high temperature.
Given that Delhi has high temperature (P(HG / HD )).

P (HD / HG ) = P(HG ∩ HD ) / P(HD )
= 0.2×0.4 / 0.2×0.4+0.5×0.1+0.3×0.01
= 0.60
Question 6 |
P: Set of Rational numbers (positive and negative)
Q: Set of functions from {0, 1} to N
R: Set of functions from N to {0, 1}
S: Set of finite subsets of N
Which of the above sets are countable?
Q and S only | |
P and S only | |
P and R only | |
P, Q and S only |
Set of functions from {0,1} to N is countable as it has one to one correspondence to N.
Set of functions from N to {0,1} is uncountable, as it has one to one correspondence to set of real numbers between (0 and 1).
Set of finite subsets of N is countable.
Question 7 |

Consider the following statements.
(I)P does not have an inverse
(II)P has a repeated eigenvalue
(III)P cannot be diagonalized
Which one of the following options is correct?
Only I and III are necessarily true | |
Only II is necessarily true | |
Only I and II are necessarily true | |
Only II and III are necessarily true |

Though the multiple of a vector represents same vector, and each eigen vector has distinct eigen value, we can conclude that ‘p’ has repeated eigen value.
If the unique eigen value corresponds to an eigen vector e, but the repeated eigen value corresponds to an entire plane, then the matrix can be diagonalized, using ‘e’ together with any two vectors that lie in plane.
But, if all eigen values are repeated, then the matrix cannot be diagonalized unless it is already diagonal.
So (III) holds correct.
A diagonal matrix can have inverse, So (I) is false.
Then (II) and (III) are necessarily True.
Question 8 |
Let c1, cn be scalars not all zero. Such that the following expression holds:

where ai is column vectors in Rn. Consider the set of linear equations.
Ax = B.where A = [a1.......an] and
Then, Set of equations has
a unique solution at x = Jn where Jn denotes a n-dimensional vector of all 1 | |
no solution | |
infinitely many solutions | |
finitely many solutions |
AX = B

As given that

means c0a0 + c1a1 + ...cnan = 0, represents that a0, a1... an are linearly dependent.
So rank of 'A' = 0, (so if ‘B’ rank is = 0 infinite solution, ‘B’ rank>0 no solution) ⇾(1)
Another condition given here is, 'Σai = b',
so for c1c2...cn = {1,1,...1} set, it is having value 'b',
so there exists a solution if AX = b →(2)
From (1)&(2), we can conclude that AX = B has infinitely many solutions.
Question 9 |
Let u and v be two vectors in R2 whose Euclidean norms satisfy ||u||=2||v||. What is the value of α such that w = u + αv bisects the angle between u and v?
2 | |
1/2 | |
1 | |
-1/2 |

Let u, v be vectors in R2, increasing at a point, with an angle θ.
A vector bisecting the angle should split θ into θ/2, θ/2
Means ‘w’ should have the same angle with u, v and it should be half of the angle between u and v.
Assume that the angle between u, v be 2θ (thus angle between u,w = θ and v,w = θ)
Cosθ = (u∙w)/(∥u∥ ∥w∥) ⇾(1)
Cosθ = (v∙w)/(∥v∥ ∥w∥) ⇾(2)
(1)/(2) ⇒ 1/1 = ((u∙w)/(∥u∥ ∥w∥))/((v∙w)/(∥v∥ ∥w∥)) ⇒ 1 = ((u∙w)/(∥u∥))/((v∙w)/(∥v∥))
⇒ (u∙w)/(v∙w) = (∥u∥)/(∥v∥) which is given that ∥u∥ = 2 ∥v∥
⇒ (u∙w)/(v∙w) = (2∥v∥)/(∥v∥) = 2 ⇾(3)
Given ∥u∥ = 2∥v∥
u∙v = ∥u∥ ∥v∥Cosθ
=2∙∥v∥2 Cosθ
w = u+αv
(u∙w)/(v∙w) = 2
(u∙(u+αv))/(v∙(u+αv)) = 2
(u∙u+α∙u∙v)/(u∙v+α∙v∙v) = 2a∙a = ∥a∥2
4∥v∥2+α∙2∙∥v∥2 Cosθ = 2(2∥v∥2 Cosθ+α∙∥v∥2)
4+2αCosθ = 2(2Cosθ+α)
4+2αCosθ = 4Cosθ+2α ⇒ Cosθ(u-v)+2α-4 = 0
4-2α = Cosθ(4-2α)
(4-2α)(Cosθ-1) = 0
4-2α = 0

Question 10 |

Consider the following statements
(i) One eigenvalue must be in [-5, 5].
(ii) The eigenvalue with the largest magnitude must be strictly greater than 5.
Which of the above statements about eigenvalues of A is/are necessarily CORRECT?
Both (I) and (II) | |
(I) only | |
(II) only | |
Neither (I) nor (II) |

be a real valued, rank = 2 matrix.

a2+b2+c2+d2 = 50
Square values are of order 0, 1, 4, 9, 16, 25, 36, …
So consider (0, 0, 5, 5) then Sum of this square = 0+0+25+25=50
To get rank 2, the 2×2 matrix can be

The eigen values are,
|A-λI| = 0 (The characteristic equation)

-λ(-λ)-25 = 0
λ2-25 = 0

So, the eigen values are within [-5, 5], Statement I is correct.
The eigen values with largest magnitude must be strictly greater than 5: False.
So, only Statement I is correct.
Question 11 |
If the characteristic polynomial of a 3 × 3 matrix M over R (the set of real numbers) is λ3 - 4λ2 + aλ + 30, a ∈ ℝ, and one eigenvalue of M is 2, then the largest among the absolute values of the eigenvalues of M is ________.
5 | |
6 | |
7 | |
8 |
λ3 - 4λ2 + aλ + 30 = 0 ⇾ (1)
One eigen value is ‘2’, so substitute it
23 - 4(2)2 + a(2) + 30 = 0
8 - 16 + 2a + 30 = 0
2a = -22
a = -11
Substitute in (1),
λ3 - 4λ2 - 11 + 30 = 0

So, (1) can be written as
(λ - 2)(λ2 - 2λ - 15) = 0
(λ - 2)(λ2 - 5λ + 3λ - 15) = 0
(λ - 2)(λ - 3)(λ - 5) = 0
λ = 2, 3, 5
Max λ=5
Question 12 |
Two eigenvalues of a 3 × 3 real matrix P are (2 + √-1) and 3. The determinant of P is __________.
18 | |
15 | |
17 | |
16 |
So, For the given 3×3 matrix there would be 3 eigen values.
Given eigen values are : 2+i and 3.
So the third eigen value should be 2-i.
As per the theorems, the determinant of the matrix is the product of the eigen values.
So the determinant is (2+i)*(2-i)*3 = 15.
Question 13 |
I. If m < n, then all such systems have a solution
II. If m > n, then none of these systems has a solution
III. If m = n, then there exists a system which has a solution
Which one of the following is CORRECT?
I, II and III are true | |
Only II and III are true | |
Only III is true | |
None of them is true |
If R(A) ≠ R(A|B)
then there will be no solution.
ii) False, because if R(A) = R(A|B),
then there will be solution possible.
iii) True, if R(A) = R(A|B),
then there exists a solution.
Question 14 |
Suppose that the eigenvalues of matrix A are 1, 2, 4. The determinant of (A-1)T is _________.
0.125 | |
0.126 | |
0.127 | |
0.128 |
Given that eigen values are 1, 2, 4.
So, its determinant is 1*2*4 = 8
The determinant of (A-1)T = 1/ AT = 1/|A| = 1/8 = 0.125
Question 15 |
In the LU decomposition of the matrix
,if the diagonal elements of U are both 1, then the lower diagonal entry l22 of L is
5 | |
6 | |
7 | |
8 |

l11 = 2 -----(1)
l11u12 = 2
u12 = 2/2
u12 = 1 ----- (2)
l21 = 4 ----- (3)
l21u12+l22 = 9
l22 = 9 - l21u12 = 9 - 4 × 1 = 5
Question 16 |
Consider the following 2 × 2 matrix A where two elements are unknown and are marked by a and b. The eigenvalues of this matrix are –1 and 7. What are the values of a and b?
a=6, b=4 | |
a=4, b=6 | |
a=3, b=5 | |
a=5, b=3 |
By properties,

⇒ 6=1+a and -7=a-4b
⇒ a=5 ⇒ -7=5-4b
⇒ b=3
Question 17 |
The larger of the two eigenvalues of the matrix is _________.
6 | |
7 | |
8 | |
9 |

⇒ λ2 - 5λ - 6 = 0 ⇒ (λ - 6)(λ + 1) = 0 ⇒ λ = 6, -1
∴ Larger eigen value is 6.
Question 18 |
Perform the following operations on the matrix
- (i) add the third row to the second row
(ii) Subtract the third column from the first column
The determinant of the resultant matrix is ________.
0 | |
1 | |
2 | |
3 |

Method 2: Determinant is unaltered by the operations (i) and (ii)
∴ Determinant of the resultant matrix = Determinant of the given matrix

(Since C1, C3 are proportional i.e., C3 = 15C1)
Question 19 |
In the given matrix, one of the eigenvalues is 1. the eigenvectors corresponding to the eigenvalue 1 are
⎡ 1 -1 2 ⎤ ⎢ 0 1 0 ⎥ ⎣ 1 2 1 ⎦
{α(4,2,1) | α≠0, α∈R} | |
{α(-4,2,1) | α≠0, α∈R} | |
{α(2,0,1) | α≠0, α∈R} | |
{α(-2,0,1) | α≠0, α∈R} |
AX = λX ⇒ (A - I)X = 0

⇒ -y+2z = 0 and x+2y = 0
⇒ y = 2z and x/(-2) = y
∴ x/(-2) = y = 2z ⇒ x/(-4) = y/2 = z/1 = α(say)

∴ Eigen vectors are {α(-4,2,1 | α≠0, α∈R}
Question 20 |
If the following system has non-trivial solution,
- px + qy + rz = 0
qx + ry + pz = 0
rx + py + qz = 0
then which one of the following options is True?
p-q+r = 0 or p = q = -r | |
p+q-r = 0 or p = -q = r | |
p+q+r = 0 or p = q = r | |
p-q+r = 0 or p = -q = -r |

Question 21 |
The value of the dot product of the eigenvectors corresponding to any pair of different eigenvalues of a 4-by-4 symmetric positive definite matrix is ________.
0 | |
1 | |
2 | |
3 |
The finite dimensional spectral theorem says that any symmetric matrix whose entries are real can be diagonalized by an orthogonal matrix.
Question 22 |
If the matrix A is such that

then the determinant of A is equal to
0 | |
1 | |
2 | |
3 |

Question 23 |
The product of the non-zero eigenvalues of the matrix
1 0 0 0 1 0 1 1 1 0 0 1 1 1 0 0 1 1 1 0 1 0 0 0 1
is ______.
6 | |
7 | |
8 | |
9 |
AX = λX

x1 + x5 = λx1 ---------- (1)
x1 + x5 = λx5 ---------- (2)
(1) + (2) ⇒ 2(x1 + x5) = λ(x1 + x5) ⇒ λ1 = 2
x2 + x3 + x4 = λ∙x2 -------- (4)
x2 + x3 + x4 = λ∙x3 -------- (5)
x2 + x3 + x4 = λ∙x4 -------- (6)
(4)+(5)+(6) = 3(x2 + x3 + x4) = λ(x2 + x3 + x4 ) ⇒ λ2 = 3
Product = λ1 × λ2 = 2×3 = 6
Question 24 |
Which one of the following statements is TRUE about every n × n matrix with only real eigenvalues?
If the trace of the matrix is positive and the determinant of the matrix is negative, at least one of its eigenvalues is negative. | |
If the trace of the matrix is positive, all its eigenvalues are positive. | |
If the determinant of the matrix is positive, all its eigenvalues are positive. | |
If the product of the trace and determinant of the matrix is positive, all its eigenvalues are positive. |
• The product of the n eigenvalues of A is the same as the determinant of A. •
A: Yes, for sum to be negative there should be atleast one negative number.
B: There can be one small negative number and remaining positive, where sum is positive.
C: Product of two negative numbers is positive. So, there no need of all positive eigen values.
D: There is no need for all eigen values to be positive, as product of two negative numbers is positive.
Question 25 |
Which one of the following does NOT equal to
![]() | |
![]() | |
![]() | |
![]() |

Try to derive options from the given matrix.
Observe that col 2 + col 3 will reuse x(x+1) term
C2 → C1 + C2



Question 26 |
Let A be the 2×2 matrix with elements a11 = a12 = a21 = +1 and a22 = -1. Then the eigenvalues of the matrix A19 are
1024 and -1024 | |
1024√2 and -1024√2 | |
4√2 and -4√2 | |
512√2 and -512√2 |
The 2×2 matrix =

Cayley Hamilton theorem:
If matrix A has ‘λ’ as eigen value, An has eigen value as λn.
Eigen value of

|A-λI| = 0

-(1-λ)(1+λ)-1 = 0
-(1-λ2 )-1 = 0
-1 = 1-λ2
λ2 = 2
λ = ±√2
A19 has (√2)19 = 29×√2 (or) (-√2)19 = -512√2
= 512√2
Question 27 |
Consider the matrix as given below.

Which one of the following provides the CORRECT values of eigenvalues of the matrix?
1, 4, 3 | |
3, 7, 3 | |
7, 3, 2 | |
1, 2, 3 |
Question 28 |
Consider the following matrix . If the eigenvalues of A are 4 and 8, then
x=4, y=10 | |
x=5, y=8 | |
x=-3, y=9 | |
x=-4, y=10 |

Trace = {Sum of diagonal elements of matrix}

Here given that eigen values are 4, 8
Sum = 8 + 4 = 12
Trace = 2 + y
⇒ 2 + y = 12
y = 10

Determinant = |2y - 3x|
Product of eigen values = 8 × 4 = 32
2y - 3x = 32
(y = 10)
20 - 3x = 32
-12 = 3x
x = -4
∴ x = -4, y = 10
Question 29 |
The following system of equations
-
x1 + x2 + 2x3 = 1
x1 + 2x2 + 3x3 = 2
x1 + 4x2 + ax3 = 4
has a unique solution. The only possible value(s) for a is/are
0 | |
either 0 or 1 | |
one of 0, 1 or -1 | |
any real number |

When a-5 = 0, then rank(A) = rank[A|B]<3,
So infinite number of solutions.
But, it is given that the given system has unique solution i.e., rank(A) = rank[A|B] = 3 will be retain only if a-5 ≠ 0.
Question 30 |
How many of the following matrices have an eigenvalue 1?
one | |
two | |
three | |
four |




Answer: We have only one matrix with eigen value 1.
Question 31 |
Let A be a 4 x 4 matrix with eigenvalues -5, -2, 1, 4. Which of the following is an eigenvalue of
[A I] [I A]
where I is the 4 x 4 identity matrix?
-5 | |
-7 | |
2 | |
1 |

|(A-λI)2-I| = 0 [a2-b2 = (a+b)(a-b)]
|(A-λI+I)(A-λI-I) = 0
|(A-(λ-I)I)(A-(λ+I)I| = 0
Let us assume:
λ-1=k & λ +1=k
λ =k+1 λ =k-1
⇓ ⇓
for k=-5; λ=-4 λ =-6
k=-2; λ=-1 λ =-3
k=1; λ=2 λ = 0
k=4; λ=5 λ = 3
So, λ = -4,-1,2,5,-6,-3,0,3
Check with the option
Option C = 2
Question 32 |
Consider the set of (column) vectors defined by X = {x ∈ R3| x1+x2+x3 = 0, where xT = [x1,x2,x3]T}. Which of the following is TRUE?
{[1,-1,0]T, [1,0,-1]T} is a basis for the subspace X. | |
{[1,-1,0]T, [1,0,-1]T} is a linearly independent set, but it does not span X and therefore is not a basis of X. | |
X is not a subspace of R3 | |
None of the above
|
Question 33 |
F is an n×n real matrix. b is an n×1 real vector. Suppose there are two n×1 vectors, u and v such that, u≠v and Fu=b, Fv=b. Which one of the following statements is false?
Determinant of F is zero | |
There are an infinite number of solutions to Fx=b | |
There is an x≠0 such that Fx=0 | |
F must have two identical rows |
Fu = Fv
Fu - Fv = 0
F(u - v) = 0
Given u ≠ v
F = 0 (i.e., Singular matrix, so determinant is zero)
Option A is true.
⇾ Fx = b; where F is singular
It can have no solution (or) infinitely many solutions.
Option B is true.
⇾ x ≠ 0 such that Fx = 0 is True because F is singular matrix (“stated by singular matrix rules). Option C is true.
⇾ F can two identical columns and rows.
Option D is false.
Question 34 |
Consider the following system of equations in three real variables xl, x2 and x3
2xl - x2 + 3x3 = 1 3xl- 2x2 + 5x3 = 2 -xl + 4x2 + x3 = 3
This system of equations has
no solution | |
a unique solution | |
more than one but a finite number of solutions | |
an infinite number of solutions
|

2(-2 - 20) +1(3 + 5) + 3(12 - 2)
= -44 + 8 + 30
= -6 ≠ 0
→ |A| ≠ 0, we have Unique Solution.
Question 35 |
What are the eigenvalues of the following 2 × 2 matrix?
|2 -1| |-4 5|
-1 and 1 | |
1 and 6 | |
2 and 5 | |
4 and -1 |

|A| = (2 - λ)(5 - λ) - (4) = 0
10 - 7λ+ λ2 - 4 = 0
λ2 - 7λ + 6 = 0
λ2 - 6λ - λ + 6 = 0
(λ - 6) -1(λ - 6) = 0
λ = 1 (or) 6
Question 36 |
The number of different n × n symmetric matrices with each element being either 0 or 1 is: (Note: power(2,x) is same as 2x)
power (2,n) | |
power (2,n2) | |
power (2, (n2 + n)/2)
| |
power (2, (n2 - n)/2)
|
A[i][j] = A[j][i]
So, we have only two choices, they are either upper triangular elements (or) lower triangular elements.
No. of such elements are
n + (n-1) + (n-2) + ... + 1
n(n+1)/2
We have two choices, thus we have
2(n(n+1)/2) = 2((n2+n)/2) choices
i.e., Power (2, (n2+n)/2).
Question 37 |
Let A, B, C, D be n × n matrices, each with non-zero determinant. If ABCD = 1, then B-1 is
D-1C-1A-1 | |
CDA
| |
ADC | |
Does not necessarily exist |
ABCD = I
Pre multiply A-1 on both sides
A-1ABCD = A-1⋅I
BCD = A-1
Pre multiply B-1 on both sides
B-1BCD = B-1A-1
CD = B-1A-1
Post multiply A on both sides
CDA = B-1A-1⋅A
∴ CDA = B-1(I)
∴ CDA = B-1
Question 38 |
How many solutions does the following system of linear equations have?
-x + 5y = -1 x - y = 2 x + 3y = 3
infinitely many | |
two distinct solutions | |
unique | |
none |

rank = r(A) = r(A|B) = 2
rank = total no. of variables
Hence, unique solution.