BoardMaths

Determinants

13 Board Maths previous year questions on Determinants — options free on every question; 1 include the answer & explanation free, the rest unlock with PYQ Pass.

Q1 FREE PREVIEW
PYQ

\(\left|\begin{array}{cc}\mathrm{x}+1 & \mathrm{x}-1 \\ \mathrm{x}^2+\mathrm{x}+1 & \mathrm{x}^2-\mathrm{x}+1\end{array}\right|\) is equal to :

a

\(2 x^3\)

b

2

c

0

d

\(2 x^3-2\)

✓ Correct answer: b)

2

Explanation

Given: \(\left|\begin{matrix}x+1 & x-1 \\ {x}^{2}+x+1 & {x}^{2}-x+1\end{matrix}\right|\)

\(=\left(x+1\right)\left({x}^{2}-x+1\right)-\left(x-1\right)\left({x}^{2}+x+1\right)\)

\(=x^3-x^2+x+x^2-x+1-(x^3+x^2+x-x^2-x-1)\)

\(=\left(x^3+1\right)-\left(x^3-1\right)=2\)

Q2
PYQ

If inverse of matrix \(\left[\begin{matrix}7 & -3 & -3 \\ -1 & 1 & 0 \\ -1 & 0 & 1\end{matrix}\right]\) is the matrix \(\left[\begin{matrix}1 & 3 & 3 \\ 1 & \lambda & 3 \\ 1 & 3 & 4\end{matrix}\right]\), then value of \(\lambda\) is:

a

\(-4\)

b

\(1\)

c

\(3\)

d

\(4\)

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Q3
PYQ

If \(\left|\begin{array}{rrr}-a & b & c \\ a & -b & c \\ a & b & -c\end{array}\right|=k a b c\), then the value of \(k\) is :

a

0

b

1

c

2

d

4

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Q4
PYQ

If inverse of matrix \(\left[\begin{matrix}7 & -3 & -3 \\ -1 & 1 & 0 \\ -1 & 0 & 1\end{matrix}\right]\) is the matrix \(\left[\begin{matrix}1 & 3 & 3 \\ 1 & \lambda & 3 \\ 1 & 3 & 4\end{matrix}\right]\), then value of \(\lambda\) is:

a

\(-4\)

b

\(1\)

c

\(3\)

d

\(4\)

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Q5
PYQ

If A is a square matrix of order 3 such that the value of \(|adj\cdot \mathrm{A}|=8\), then the value of \(\left|{\mathrm{A}}^{\mathrm{T}}\right|\) is :

a

\(\sqrt{2}\)

b

\(-\sqrt{2}\)

c

\(8\)

d

\(2\sqrt{2}\)

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Q6
PYQ

If \(A\) is a square matrix of order \(3\) such that the value of \(|adj\cdot \mathrm{A}|=8\), then the value of \(\left|{\mathrm{A}}^{\mathrm{T}}\right|\) is :

a

\(\sqrt{2}\)

b

\(-\sqrt{2}\)

c

\(8\)

d

\(2\sqrt{2}\)

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Q7
PYQ

If \(\left|\begin{array}{rrr}-a & b & c \\ a & -b & c \\ a & b & -c\end{array}\right|=k a b c\), then the value of \(k\) is :

a

0

b

1

c

2

d

4

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Q8
PYQ

\(\left|\begin{array}{cc}\mathrm{x}+1 & \mathrm{x}-1 \\ \mathrm{x}^2+\mathrm{x}+1 & \mathrm{x}^2-\mathrm{x}+1\end{array}\right|\) is equal to :

a

\(2 x^3\)

b

2

c

0

d

\(2 x^3-2\)

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Q9
PYQ

If A is an invertible matrix of order 2 , then \(\det \left({A}^{-1}\right)\) is equal to :

a

\(\det (A)\)

b

\(\frac{1}{\det (A)}\)

c

1

d

0

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Q10
PYQ

If A is a nonsingular square matrix of order \(3\times 3\) and \(|A|=2\), then \(|adjA|\) is equal to -

a

4

b

2

c

8

d

0

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Q11
PYQ

If A is a square matrix of order \(2\times 2\), then \(|5A|\) is equal to

a

\(5|A|\)

b

\(25|\mathrm{A}|\)

c

\(125|A|\)

d

\(15|A|\)

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Q12
PYQ

Assertion (A) : For matrix \(\mathrm{A}=\left[\begin{array}{ccc}1 & \cos \theta & 1 \\ -\cos \theta & 1 & \cos \theta \\ -1 & -\cos \theta & 1\end{array}\right]\), where \(\theta \in[0,2 \pi]\), \(|\mathrm{A}| \in[2,4]\).
Reason \((R): \quad \cos \theta \in[-1,1], \forall \theta \in[0,2 \pi]\).

a

Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of the Assertion (A).

b

Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of the Assertion (A).

c

Assertion (A) is true, but Reason (R) is false.

d

Assertion (A) is false, but Reason (R) is true.

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Q13
PYQ

If \(\left|\begin{matrix}x & 2 \\ 18 & x\end{matrix}\right|=0\), then x is equal to

a

6

b

\(\pm 6\)

c

-6

d

0

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