Mathematics (NDA/NA SOLVED PAPER 2021-I) (01 to 50)

Total Questions: 50

11. If A and B are two matrices such that AB is of order n × n, then which one of the following is correct?

Correct Answer: (d) Orders of A and B need not be the same.
Solution:Hence, order of A and B need not to be same.

12. How many matrices of different orders are possible with elements comprising all prime numbers less than 30?

Correct Answer: (c) 4
Solution:Prime number less than 30 are
2, 3, 5, 7, 11, 13, 17, 19, 23 and 29.
Number of prime number = 10.
Different order of matrices:
1 × 10, 10 × 1, 2 × 5, and 5 × 2.

13. Find the value?

Correct Answer: (c) 317
Solution:

14. If A and B are square matrices of order 2 such that det(AB) = det(BA), then which one of the following is correct?

Correct Answer: (d) A and B need not be unit matrices.
Solution:

15. What is cot 2x cot 4x - cot 4x cot 6x - cot 6x cot 2x equal to?

Correct Answer: (c) 1
Solution:

16. If tan x = - 3/4 and x is in the second quadrant, then what is the value of sin x .cos x ?

Correct Answer: (d) - 12/25
Solution:

17. What is the value of the following?

Correct Answer: (c) -4
Solution:

18. Find the value?

Correct Answer: (c) -1 or 1
Solution:

19. What is the value of the following?

tan 31° tan 33° tan 35°______tan 57°  tan 59°

Correct Answer: (c) 1
Solution:

20. Find the value?

Correct Answer: (a) 0
Solution: