NDA & NA Exam (I)- 2025 - Mathematics Defence Question Paper

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NDA & NA Exam (I)- 2025 - Mathematics

NDA & NA Exam (I)- 2025 - Mathematics Defence Questions

21.
If the sum of binomial coefficients in the expansion of \( (x + y)^{n} \) is 256, then the greatest binomial coefficient occurs in which one of the following terms?
A.
Third
B.
Fourth
C.
Fifth
D.
Ninth
ANSWER :
C. Fifth
22.
If \( k < \left(\sqrt{2} + 1\right)^{3} < k + 2 \), where \( k \) is a natural number, then what is the value of \( k \)?
A.
11
B.
13
C.
15
D.
17
ANSWER :
B. 13
23.
If
\( \begin{bmatrix} x & 1 & 1 \end{bmatrix} \begin{bmatrix} 1 & 2 & 3 \\ 4 & 5 & 6 \\ 7 & 8 & 9 \end{bmatrix} \begin{bmatrix} 1 \\ 1 \\ x \end{bmatrix} = \begin{bmatrix} 45 \end{bmatrix} \)
then which one of the following is a value of \( x \)?
A.
-2
B.
-1
C.
0
D.
1
ANSWER :
D. 1
24.
If
\( A = \begin{bmatrix} y & z & x \\ z & x & y \\ x & y & z \end{bmatrix} \)
where \( x, y, z \) are integers, is an orthogonal matrix, then what is the value of \( x^{2} + y^{2} + z^{2} \)?
A.
0
B.
1
C.
4
D.
14
ANSWER :
B. 1
25.
Consider the following in respect of a non-singular matrix \( M \):
I. \( |M^{2}| = |M|^{2} \)
II. \( |M| = |M^{-1}| \)
III. \( |M| = |M^{T}| \)
How many of the above are correct?
A.
None
B.
One
C.
Two
D.
All three
ANSWER :
C. Two
26.
If
\( f(\theta) = \begin{bmatrix} \cos \theta & \sin \theta \\ -\sin \theta & \cos \theta \end{bmatrix} \)
then what is \( \left\{f(\pi)\right\}^{2} \) equal to?
A.
\( \begin{bmatrix} -1 & 0 \\ 0 & -1 \end{bmatrix} \)
B.
\( \begin{bmatrix} 1 & 1 \\ 1 & 1 \end{bmatrix} \)
C.
\( \begin{bmatrix} -1 & 0 \\ 0 & 1 \end{bmatrix} \)
D.
\( \begin{bmatrix} 1 & 0 \\ 0 & 1 \end{bmatrix} \)
ANSWER :
D. \( \begin{bmatrix} 1 & 0 \\ 0 & 1 \end{bmatrix} \)
27.
If
\( A = \begin{bmatrix} 1 & 2 & 2 \\ 2 & 1 & 2 \\ 2 & 2 & 1 \end{bmatrix} \)
then what is \( A^{2} - 4A \) equal to?
where \( I_{3} \) is the identity matrix of order 3.
A.
\( -5I_{3} \)
B.
\( -I_{3} \)
C.
\( I_{3} \)
D.
\( 5I_{3} \)
ANSWER :
D. \( 5I_{3} \)
28.
If the number of selections of \( r \) as well as \( (n + r) \) things from \( 5n \) different things are equal, then what is the value of \( r \)?
A.
\( n \)
B.
\( 2n \)
C.
\( 3n \)
D.
\( 4n \)
ANSWER :
B. \( 2n \)
29.
What is the number of selections of at most 3 things from 6 different things (including the selection of none)?
A.
20
B.
22
C.
41
D.
42
ANSWER :
D. 42
30.
If
\( A = \begin{bmatrix} x & y & z \\ y & z & x \\ z & x & y \end{bmatrix} \)
where \( x, y, z \) are integers, is an orthogonal matrix, then what is \( A^{2} \) equal to?
A.
Null matrix
B.
Identity matrix
C.
\( A \)
D.
\( -A \)
ANSWER :
B. Identity matrix