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NCERT Solutions for class 11 Maths | Chapter 3 - Trigonometric Functions

(1) In a triangle ABC, cosec A (sin B cos C + cos B sin C) equals
[A] none of these
[B] c/a
[C] 1
[D] a/c
Answer: 1
(2) The perimeter of a triangle ABC is 6 times the arithmetic mean of the sines of its angles. If the side b is 2, then the angle B is
[A] 30°
[B] 90°
[C] 60°
[D] 120°
Answer: 90°

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(3) If cos a + 2cos b + cos c = 2 then a, b, c are in
[A] 2b = a + c
[B] b² = a × c
[C] a = b = c
[D] None of these
Answer: 2b = a + c
(4) If tan A – tan B = x and cot B – cot A = y, then the value of cot (A – B) is
[A] x + y
[B] 1/x + y
[C] x + 1/y
[D] 1/x + 1/y
Answer: 1/x + 1/y
(5) If cos a + 2cos b + cos c = 2 then a, b, c are in
[A] 2b = a + c
[B] b² = a × c
[C] a = b = c
[D] None of these
Answer: 2b = a + c
(6) The value of 4 × sin x × sin(x + π/3) × sin(x + 2π/3) is
[A] sin x
[B] sin 2x
[C] sin 3x
[D] sin 4x
Answer: sin 3x
(7) The value of cos 20 + 2sin² 55 – √2 sin65 is
[A] 0
[B] 1
[C] -1
[D] None of these
Answer: 1
(8) If the angles of a triangle be in the ratio 1 : 4 : 5, then the ratio of the greatest side to the smallest side is
[A] 4 : (√5 – 1)
[B] 5 : 4
[C] (√5 – 1) : 4
[D] none of these
Answer: 4 : (√5 – 1)
(9) If 3 × tan(x – 15) = tan(x + 15), then the value of x is
[A] 30
[B] 45
[C] 60
[D] 90
Answer: 45
(10) The value of cos 5π is
[A] 0
[B] 1
[C] -1
[D] None of these
Answer: -1
(11) The value of cos² x + cos² y – 2cos x × cos y × cos (x + y) is
[A] sin (x + y)
[B] sin² (x + y)
[C] sin³ (x + y)
[D] sin4 (x + y)
Answer: sin² (x + y)
(12) The value of (sin 7x + sin 5x) /(cos 7x + cos 5x) + (sin 9x + sin 3x) / (cos 9x + cos 3x) is
[A] tan 6x
[B] 2 tan 6x
[C] 3 tan 6x
[D] 4 tan 6x
Answer: 2 tan 6x
(13) The value of tan 20 × tan 40 × tan 80 is
[A] tan 30
[B] tan 60
[C] 2 tan 30
[D] 2 tan 60
Answer: tan 60
(14) If the angles of a triangle be in the ratio 1 : 4 : 5, then the ratio of the greatest side to the smallest side is
[A] 4 : (√5 – 1)
[B] 5 : 4
[C] (√5 – 1) : 4
[D] none of these
Answer: 4 : (√5 – 1)
(15) If a×cos x + b × cos x = c, then the value of (a × sin x – b²cos x)² is
[A] a² + b² + c²
[B] a² – b² – c²
[C] a² – b² + c²
[D] a² + b² – c²
Answer: a² + b² – c²
(16) The value of cos 180° is
[A] 0
[B] 1
[C] -1
[D] infinite
Answer: -1
(17) If the sides of a triangle are 13, 7, 8 the greatest angle of the triangle is
[A] π/3
[B] π/2
[C] 2π/3
[D] 3π/2
Answer: 2π/3
(18) The general solution of √3 cos x – sin x = 1 is
[A] x = n × π + (-1)n × (π/6)
[B] x = π/3 – n × π + (-1)n × (π/6)
[C] x = π/3 + n × π + (-1)n × (π/6)
[D] x = π/3 – n × π + (π/6)
Answer: x = π/3 + n × π + (-1)n × (π/6)
(19) If tan² θ = 1 – e², then the value of sec θ + tan³ θ × cosec θ is
[A] 2 – e²
[B] (2 – e²)1/2
[C] (2 – e²)²
[D] (2 – e²)3/2
Answer: (2 – e²)3/2
(20) If the radius of the circumcircle of an isosceles triangle PQR is equal to PQ ( = PR), then the angle P is
[A] 2π/3
[B] π/3
[C] π/2
[D] π/6
Answer: 2π/3

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