NDA & NA Exam (I)- 2021 - Mathematics Defence Question Paper

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NDA & NA Exam (I)- 2021 - Mathematics

NDA & NA Exam (I)- 2021 - Mathematics Defence Questions

31.
\( \tan^{-1} x + \cot^{-1} x = \frac{\pi}{2} \) holds, when
A.
\( x \in \mathbb{R} \)
B.
\( x \in \mathbb{R} - (-1, 1) \) only
C.
\( x \in \mathbb{R} - \{0\} \) only
D.
\( x \in \mathbb{R} - [-1, 1] \) only
ANSWER :
A. \( x \in \mathbb{R} \)
32.
If \( \tan A = \frac{1}{7} \), then what is \( \cos 2A \) equal to?
A.
\( \frac{24}{25} \)
B.
\( \frac{18}{25} \)
C.
\( \frac{12}{25} \)
D.
\( \frac{6}{25} \)
ANSWER :
A. \( \frac{24}{25} \)
33.
The sides of a triangle are \( m, n \) and \( \sqrt{m^{2} + n^{2} + mn} \). What is the sum of the acute angles of the triangle?
A.
\( 45^{\circ} \)
B.
\( 60^{\circ} \)
C.
\( 75^{\circ} \)
D.
\( 90^{\circ} \)
ANSWER :
B. \( 60^{\circ} \)
34.
What is the area of the triangle \( ABC \) with sides \( a = 10 \) cm, \( c = 4 \) cm and angle \( B = 30^{\circ} \)?
A.
16 cm2
B.
12 cm2
C.
10 cm2
D.
8 cm2
ANSWER :
C. 10 cm2
35.
Consider the following statements:
1. \( A = \{1, 3, 5\} \) and \( B = \{2, 4, 7\} \) are equivalent sets.
2. \( A = \{1, 5, 9\} \) and \( B = \{1, 5, 5, 9, 9\} \) are equal sets.
Which of the above statements is/are correct?
A.
1 only
B.
2 only
C.
Both 1 and 2
D.
Neither 1 nor 2
ANSWER :
C. Both 1 and 2
36.
Consider the following statements:
1. The null set is a subset of every set.
2. Every set is a subset of itself.
3. If a set has 10 elements, then its power set will have 1024 elements.
Which of the above statements are correct?
A.
1 and 2 only
B.
2 and 3 only
C.
1 and 3 only
D.
1, 2 and 3
ANSWER :
D. 1, 2 and 3
37.
Let \( R \) be a relation defined as \( xRy \) if and only if \( 2x + 3y = 20 \), where \( x, y \in \mathbb{N} \). How many elements of the form \( (x, y) \) are there in \( R \)?
A.
2
B.
3
C.
4
D.
6
ANSWER :
B. 3
38.
Consider the following statements:
1. A function \( f: \mathbb{Z} \rightarrow \mathbb{Z} \), defined by \( f(x) = x + 1 \), is one-one as well as onto.
2. A function \( f: \mathbb{N} \rightarrow \mathbb{N} \), defined by \( f(x) = x + 1 \), is one-one but not onto.
Which of the above statements is/are correct?
A.
1 only
B.
2 only
C.
Both 1 and 2
D.
Neither 1 nor 2
ANSWER :
C. Both 1 and 2
39.
Consider the following in respect of a complex number \( Z \):
1. \( \overline{(Z^{-1})} = (\bar{Z})^{-1} \)
2. \( Z\bar{Z} = |Z|^{2} \)
Which of the above is/are correct?
A.
1 only
B.
2 only
C.
Both 1 and 2
D.
Neither 1 nor 2
ANSWER :
C. Both 1 and 2
40.
Consider the following statements in respect of an arbitrary complex number \( Z \):
1. The difference of \( Z \) and its conjugate is zero or a purely imaginary number.
2. The sum of \( Z \) and its conjugate is a real number.
Which of the above statements is/are correct?
A.
1 only
B.
2 only
C.
Both 1 and 2
D.
Neither 1 nor 2
ANSWER :
C. Both 1 and 2