Question:
What is (pq +qr + rp) equal to?
What is (pq +qr + rp) equal to?
Options:
- a) -3 4
- b) 0
- c) 1 4
- d) 3 4
- a) -3 4
- b) 0
- c) 1 4
- d) 3 4
correct answer : a)
Explanation:
pq + qr + rp = q(p + r) + rp
= -q2 + rp = – sin2 25° – sin 95°. sin 35°
(\ p + q + r = 0)
Oswaal NDA/NA Year-wise Solved Papers
= 1
2
[- 2sin225° – 2sin 95°. sin 35°]
=
1
2
[- 1 + cos 50° + cos 130° – cos 60°]
= 1
2
[- 1 + cos 50° – cos 50°- 1
2
]
= -3
4
pq + qr + rp = q(p + r) + rp
= -q2 + rp = – sin2 25° – sin 95°. sin 35°
(\ p + q + r = 0)
Oswaal NDA/NA Year-wise Solved Papers
= 1
2
[- 2sin225° – 2sin 95°. sin 35°]
=
1
2
[- 1 + cos 50° + cos 130° – cos 60°]
= 1
2
[- 1 + cos 50° – cos 50°- 1
2
]
= -3
4