Trigonometry MCQ
1) Which of the following is the correct value of cot 100.cot 200.cot 600.cot 700.cot 800?
- 1/√3
- √3
- -1
- 1
Answer: (a) 1/√3
Explanation: Here, we can apply the formula –
cot A. cot B = 1 (when A + B = 900)
= (cot 200 . cot 700) x (cot 100 . cot 800) x cot 600
= 1 x 1 x 1/√3
= 1/√3
So, the correct value of cot 100.cot 200.cot 600.cot 700.cot 800 = 1/√3
2) If a sin 450 = b cosec 300, what is the value of a4/b4?
- 63
- 43
- 23
- None of the above
Answer: (b) 43
Explanation: Given a sin 450 = b cosec 300
So, a/b = cosec 300/ sin 450
a/b = 2/( 1/√2)
a/b = 2√2/1
a4/b4 = (2√2/1)4
a4/b4 = 64/1
or,
a4/b4 = 43
3) If tan θ + cot θ = 2, then what is the value of tan100 θ + cot100 θ?
- 1
- 3
- 2
- None of the above
Answer: (c) 2
Explanation: Given tan θ + cot θ = 2
Put θ = 450, above equation will satisfy as,
1 + 1 = 2
So, θ = 450,
= tan100 450 + cot100 450
= 1100 + 1100
= 2
4) If the value of α + β = 900, and α : β = 2 : 1, then what is the ratio of cos α to cos β ?
- 1 : 3
- √3 : 1
- 1 : √3
- None of the above
Answer: (c) 1 : √3
Explanation: Given α + β = 900, and α : β = 2 : 1
So, we can say that 2x + x = 900
3x = 900, which give
x = 300
So, α = 2x = 60
β = x = 30
cos α / cos β = cos 600 / cos 300
=> (1/2) / (√3/2)
or, 1/2 * 2/√3
= 1/√3
Or the ratio between cos α : cos β = 1 : √3
5) If θ is said to be an acute angle, and 7 sin2 θ + 3 cos2 θ = 4, then what is the value of tan θ?
- 1
- √3
- 1/√3
- None of the above
Answer: (c) 1/√3
Explanation: Given 7 sin2 θ + 3 cos2 θ = 4
=> 7 sin2 θ + 3 (1 – sin2 θ) = 4
=> 7 sin2 θ + 3 – 3sin2 θ = 4
Then, 4sin2 θ = 1
Or, sin θ = 1/2
So, θ = 300
Now, put θ = 300 in tan θ, we will get,
tan θ = 1/√3
Alternate
We can directly check the equation by putting values of θ. Let’s put θ = 300
7 sin2 300 + 3 cos2 300= 4
Then, 7 * 1/4 + 3 * 3/4 = 4
So, 7/4 + 9/4 = 4
16/4 = 4
Or, 4 = 4 (so, it satisfy the condition)
Now, tan 300 = 1/√3
6) If tan θ – cot θ = 0, what will be the value of sin θ + cos θ?
- 1
- √2
- 1/√2
- None of the above
Answer: (b) √2
Explanation: Given tan θ – cot θ = 0
Let’s put θ = 450 in order to satisfy the above equation
tan 450 – cot 450 = 0
1 – 1 = 0 (equation satisfied with θ = 450)
Now, put θ = 450 in sin θ + cos θ, we will get
= sin 450 + cos 450
= 1/√2 + 1/√2
= √2
7) If θ is said to be an acute angle, and 4 cos2 θ – 1 = 0, then what is the value of tan (θ – 150)?
- 1
- √2
- 1/√3
- None of the above
Answer: (a) 1
Explanation: Given 4 cos2 θ – 1 = 0
4 cos2 θ = 1
cos2 θ = 1/4
cos θ = 1/2
Or, θ = 600
So, tan (θ – 150) = ?
=> tan (600 – 150)
= tan 450
= 1
8) If the value of θ + φ = π/2, and sin θ = 1/2, what will be the value of sinφ?
- 1
- √2
- √3/2
- 2/√3
Answer: (c) √3/2
Explanation: Given θ + φ = π/2
It can be written as, θ + φ = 900 (as π = 1800) …….(i)
sin θ = 1/2
or, θ = 300
On putting the value of θ = 300 in equation (i), we will get,
300 + φ = 900
So, φ = 600
Then, sin φ = sin 600 = √3/2
9) What will be the value of 2cos2 θ – 1, if cos4 θ – sin4 θ = 2/3?
- 1
- 2
- 3/2
- 2/3
Answer: (d) 2/3
Explanation: Given cos4 θ – sin4 θ = 2/3
Now, here we can apply the formula –
a4 – b4 = (a2 – b2) (a2 + b2)
So, (cos2 θ – sin2 θ) (cos2 θ + sin2 θ) = 2/3
So, 1 x (cos2 θ – sin2 θ) = 2/3 (because cos2 θ + sin2 θ = 1)
=> cos2 θ – (1 – cos2 θ) = 2/3 (because sin2 θ = 1 – cos2 θ)
So, 2cos2 θ – 1 = 2/3
10) What will be the value of 1 – 2sin2 θ, if cos4 θ – sin4 θ = 2/3?
- 1
- 2
- 3/2
- 2/3
Answer: (d) 2/3
Explanation: Given cos4 θ – sin4 θ = 2/3
Now, here we can apply the formula –
a4 – b4 = (a2 – b2) (a2 + b2)
So, (cos2 θ – sin2 θ) (cos2 θ + sin2 θ) = 2/3
So, 1 x (cos2 θ – sin2 θ) = 2/3 (because cos2 θ + sin2 θ = 1)
=> (1 – sin2 θ) – sin2 θ = 2/3
So, 1 – 2sin2 θ = 2/3
11) What is the value of tan θ/(1 – cot θ) + cot θ/(1 – tan θ)?
- tan θ + cot θ + 1
- tan θ – cot θ – 1
- tan θ – cot θ + 1
- None of the above
Answer: (a) tan θ + cot θ + 1
Explanation: tan θ/(1 – (1/tan θ) + (1/tan θ)/(1 – tan θ)
= tan2 θ/ (tan θ – 1) – 1/tan θ(tan θ – 1)
= tan3 θ – 1/tan θ(tan θ – 1)
Apply the formula, a3– b3 = (a – b) (a2 + ab + b2)
= (tan θ – 1) (tan2 θ + tan θ + 1) / tan θ(tan θ – 1)
= (tan2 θ + tan θ + 1) / tan θ
On taking tan θ common from the numerator, we will get,
= tan θ + cot θ + 1
12) What is the value of sin θ/(1 + cos θ) + sin θ/(1 – cos θ), where (00 < θ < 900)?
- 2cosec θ
- 2tan θ
- 2cot θ
- None of the above
Answer: (a) 2cosec θ
Explanation: Given, sin θ/(1 + cos θ) + sin θ/(1 – cos θ)
= [sin θ (1 – cos θ) + sin θ (1 + cos θ)] / [(1 – cos θ) (1 + cos θ)]
= [sin θ – sin θ cos θ + sin θ + sin θ cos θ] / [1 – cos2 θ]
= 2 sin θ / sin2 θ
= 2 cosec θ
13) What will be the value of (√3 tanθ + 1), if r sinθ = 1, and r cosθ = √3?
- 2
- 1
- 0
- None of the above
Answer: (a) 2
Explanation: Given, r sinθ = 1, and r cosθ = √3
r sinθ / r cosθ = 1/√3
tanθ = 1/√3
or √3 tanθ = 1
So, √3 tanθ + 1= 1 + 1
= 2
14) What is the value of (tan2 θ – sec2 θ)?
- 2
- -1
- 1
- None of the above
Answer: (b) -1
Explanation: (tan2 θ – sec2 θ)
= sin2 θ/cos2 θ – 1/cos2 θ
= (sin2 θ – 1) / cos2 θ
= – cos2 θ/cos2 θ
= -1
15) If sin θ = 0.7, then what is the value of cosθ, if 00 <= θ < 900?
- √51
- √49
- 0.3
- None of the above
Answer: (a) √0.51
Explanation: Given sin θ = 0.7
As we know, sin2 θ + cos 2 θ = 1
So, (0.7)2 + cos 2 θ = 1
Then, 0.49 + cos 2 θ = 1
=> cos2 θ = 1 – 0.49
cos θ = √0.51
16) What is the value of tan3θ, If tan7θ.tan2θ = 1?
- √3
- 1/√3
- -1/√3
- None of the above
Answer: (b) 1/√3
Explanation: Given tan7θ.tan2θ = 1
As we know, if tanA . tanB = 1 then, A + B = 900
So, 7θ + 3θ = 900
=> 9θ = 900
Or, θ = 100
Now, we have to find tan3θ
So, put θ = 100 in tan3θ, we will get
tan 300 = 1/√3
17) What will be the value of 3cos800.cosec100 + 2cos590.cosec310?
- 3
- 1
- 5
- None of the above
Answer: (c) 5
Explanation: 3cos800.cosec100 + 2cos590.cosec310 = ?
According to the identity, [if A + B = 900 then, cosA.cosecB = 1]
So, 3cos800.(1/sin100) + 2cos590.(1/sin310)
= 3cos800.(1/sin(900 – 800)) + 2cos590.(1/sin(900 – 590))
=> 3cos800/cos 800) + 2cos590/cos 590 ( because sin (900 – θ) = cos θ)
= 3 + 2
= 5
18) If sin (θ + 180) = cos 600, then what is the value of cos5θ, where 00 < θ < 900?
- 0
- 1/2
- 1
- 2
Answer: (b) 1/2
Explanation: Given sin (θ + 180) = cos 600
sin (θ + 180) = cos (900 – 300)
So, sin (θ + 180) = sin300
Then, θ = 300 – 180
θ = 120
So, cos5θ = cos 5 x 120
= cos 600
= 1/2
19) If cos A = 2/3, then what is the value of tan A?
- 0
- 1/2
- 5/2
- √5/2
Answer: (d) √5/2
Explanation: According to the trigonometric identities,
1 + tan2 A = sec2 A
And we know, sec A = 1/cos A
So, sec A = 1/(2/3) = 3/2
Then, 1 + tan2 A = (3/2)2 = 9/4
=> tan2 A = 9/4 – 1
=> tan2 A = 5/4
So, tan A = √5/2
20) What will be the simplified value of (sec A sec B + tan A tan B)2 – ( sec A tan B + tan A sec B)2?
- 0
- 1
- -1
- 2
Answer: (b) 1
Explanation: The question is in the form of (a + b)2
So, on applying the identity, and after expanding the given equation, we will get –
=> sec2 A sec2 B + tan2 A tan2 B + 2 sec A sec B tan A tan B – sec2 A tan2 B – tan2 A sec2 B – 2 sec A tan B tan A sec B
=> Then, sec2 A [sec2 B – tan2 B] – tan2 A [sec2 B – tan2 B]
So, it will be written as [sec2 A – tan2 A] [sec2 B – tan2 B]
= 1 x 1
= 1.
21) What is the simplified value of (cosec A – sin A)2 + (sec A – cos A)2 – (cot A – tan A)2?
- 0
- 1
- -1
- 2
Answer: (b) 1
Explanation: The question is in the form of (a – b)2
(a – b)2 = a2 + b2 – 2ab
So, on applying the identity, and after expanding the given equation, we will get –
=> cosec2 A + sin2 A – 2 cosec A sin A + sec2 A + cos2 A – 2 sec A cos A – cot2 A – tan2 A + 2 cot A tan A
After solving it with using trigonometric identities, we will get –
=> (cosec2 A – cot2 A) + (sin2 A + cos2 A) + (sec2 A – tan2 A) -2
= 1 + 1 + 1 – 2
= 3 – 2
= 1
Alternate method
(cosec A – sin A)2 + (sec A – cos A)2 – (cot A – tan A)2
We can solve it directly by putting θ = 450
= (cosec 450 – sin 450)2 + (sec 450 – cos 450)2 – (cot 450 – tan 450)2
= (√2 – 1/√2)2 + (√2 – 1/√2)2 – (1 – 1)2
= 1/2 + 1/2 – 0
= 1
22) What will be the value of sec4 θ – tan4 θ, if sec2 θ + tan2 θ = 7/12?
- 1/2
- 7/12
- 1
- 2/3
Answer: (b) 7/12
Explanation: Given sec2 θ + tan2 θ = 7/12
Now, here we can apply the formula –
a4 – b4 = (a2 – b2) (a2 + b2)
sec4 θ – tan4 θ = (sec2 θ – tan2 θ) (sec2 θ + tan2 θ)
= 1 x (sec2 θ + tan2 θ) {because 1 + tan2 θ = sec2 θ}
= 1 x 7/12
= 7/12
23) What is the value of cos2 200 + cos2 700?
- √2
- 0
- 1
- None of the above
Answer: (c) 1
Explanation: cos2 200 + cos2 700
We can write cos2 200 as cos2 (900 – 700)
So, cos2 (900 – 700) + cos2 700
= sin2 700 + cos2 700
= 1
24) If r cosθ = √3, and r sinθ = 1, what is the value of r2 tanθ?
- 4/√3
- √3/4
- √3
- None of the above
Answer: (a) 4/√3
Explanation: Given r cosθ = √3, and r sinθ = 1
r cosθ / r sinθ = 1/√3
tanθ = tan 300
Or, θ = 300
On putting, θ = 300, we will get,
r sin 300 = 1
r x ½ = 1
or r =2
Now, r2 tanθ = ?
= (2)2 tan 300
= 4 x 1/√3
= 4/√3
25) Which of the following is the correct value of tan2 A + cot2 A – sec2 A cosec2 A, where 00 < A < 900?
- 4
- 2
- -2
- None of the above
Answer: (c) -2
Explanation: We can solve it by putting θ = 450
On putting θ = 450, we will get –
= tan2 450 + cot2 450 – sec2 450 cosec2 450
= 1 + 1 – (√2)2 x (√2)2
= 2 – 4
= -2
26) If the value of tan2 θ + tan4 θ = 1, what will be the value of cos2 θ + cos4 θ?
- 4
- 1
- -2
- -1
Answer: (b) 1
Explanation: Given, tan2 θ + tan4 θ = 1 …. (i)
From equation (i),
tan2 θ ( 1 + tan2 θ ) = 1
tan2 θ ( sec2 θ ) = 1 [As according to the trigonometric identity, sec2 θ – tan2 θ = 1]
tan2 θ = 1/ sec2 θ
tan2 θ = cos2 θ ….(ii)
Now, cos2 θ + cos4 θ = ?
=> cos2 θ + (cos2)2 θ
=> tan2 θ + (tan2)2 θ
=> tan2 θ + tan4 θ
= 1 {from equation (i)}
27) If 4sin2 θ = 3, and θ is a positive acute angle, what is the value of tan θ – cot θ/2?
- 4
- 0
- -2
- -1
Answer: (b) 0
Explanation: Given, 4 sin2 θ = 3
Or, sin2 θ = 3/4
Or, sin θ = √3/2
So, θ = 600
Now, tan θ – cot θ/2 = ?
Put θ = 600
= tan 600 – cot 600/2
= tan 600 – cot 300
= √3 – √3
= 0
28) If the value of sin A + cosec A = 2, then what is the value of sin7 A + cosec7 A?
- 1
- 0
- 2
- 3
Answer: (c) 2
Explanation: It is given that sin A + cosec A = 2 ……(i)
On putting A = 900, then above condition will satisfy
sin 900 + cosec 900 = 2
or, 1 + 1 = 2 (as the equation satisfies, so, A = 900)
Now, sin7 A + cosec7 A = ?
=> sin7 900 + cosec7 900
=> 17 + 17
= 2
29) What is the value of (2tan 300) / (1 + tan2 300)?
- cos 450
- cos 900
- sin 600
- sin 300
Answer: (c) sin 600
Explanation: tan 300 = 1/√3
(2tan 300) / (1 + tan2 300) = ?
= (2 x 1/√3) / (1 + (1/√3)2)
= (2/√3) / (4/3)
= 6/4√3
= Or √3/2, which is equal to option C, i.e., sin600.
30) What is the value of (sin 300 + cos 600) – (sin 600 + cos 300)?
- 1 + √2
- 1 + 2√2
- 1 + √3
- 1 + 2√3
Answer: (c) 1 + √3
Explanation: Let’s see the values –
sin 300 = 1/2
cos 600 = 1/2
sin 600 = √3/2
cos 300 = √3/2
So, (1/2 + 1/2) – (√3/2 + √3/2)
= 1 – 2√3/2
Or, 1 – √3
31) If 1 + cos2 θ is equal to 3 sin θ.cos θ, then what is the value of cot θ?
- 1
- 0
- 2
- 3
Answer: (a) 1
Explanation: It is given that, 1 + cos2 θ = 3 cos θ.sin θ
On dividing both sides by sin2 θ, we will get
1+cos2 θ / sin2 θ = 3 cos θ.sin θ/sin2 θ
cosec2 θ + cot2 θ = 3 cot θ
=> 1 + cot2 θ + cot2 θ = 3 cot θ [because 1 + cot2 θ = cosec2 θ]
=> 1 + 2cot2 θ = 3 cot θ
=> 2 cot2 θ = 3 cot θ – 1
Let’s try to put θ = 450
=> 2cot2 450 – 3 cot 450 + 1 = 0
=> 2 -3 + 1 = 0
=> 0 = 0 (satisfies)
So, θ = 450
cot θ = cot 450
= 1
32) If the value of tan θ = 4/3, then which of the following is the correct value of (3 sin θ + 2 cos θ) / (3 sin θ – 2 cos θ) =?
- 1
- -3
- 2
- 3
Answer: (d) 3
Explanation: It is given that, tan θ = 4/3
=> sin θ / cos θ = 4/3
So sin θ = 4, and cos θ = 3
Now, on putting the values of sin θ and cos θ in (3 sin θ + 2 cos θ) / (3 sin θ – 2 cos θ), we will get –
= 3×4 + 2×3/ 3×4 – 2×3
= 18/6
= 3
33) If the value of tan 150 is 2 – √3, then what is the value of tan 150 cot 750 + tan 750 cot 150?
- 14
- -13
- 21
- -14
Answer: (a) 14
Explanation: tan 150 cot 750 + tan 750 cot 150 = ?
tan 150 cot (900 – 150) + tan (900 – 150) cot 150 [as cot (900 – θ) = tan θ, and tan (900 – θ) = cot θ]
= tan2 150 + cot2 150 …..(i)
cot 150 = 1/tan 150
= 1 / 2-√3
= (1 / 2-√3) x (2+√3 / 2+√3)
So, cot 150 = 2 + √3
So, on putting the values of cot 150 and tan 150 in equation (i), we will get
= (2 – √3)2 + (2 + √3)2
= 4 + 3 – 2√3 + 4 + 3 + 2√3
= 14
34) Which of the following is the correct relation between A and B, if A = tan 110 . tan 290, and B = 2 cot 610 . cot 790?
- A = B
- A = -B
- A = 2B
- 2A = B
Answer: (d) 2A = B
Explanation: Given A = tan 110 . tan 290, and B = 2 cot 610 . cot 790
A / B = tan 110 . tan 290 / 2 cot 610 . cot 790
= [tan 110 . tan 290] / [2 cot (900 – 290) . cot (900 – 110)]
= tan 110 . tan 290 / 2 tan 110 . tan 290
= 1/2
So, A/B = 1/2
Or, 2A = B
35) If sin θ x cos θ = 1/2, then what is the value of sin θ – cos θ?
- 0
- 1
- -1
- None of the above
Answer: (a) 0
Explanation: Given sin θ x cos θ = 1/2
On multiplying both sides by 2, we will get –
2 sin θ x cos θ = 1
sin 2θ = 1 (because sin 2θ = 2 sinθ cosθ)
So, 2θ = 900
=> θ = 450
Therefore, sin θ – cos θ = ?
=> sin 450 – cos 450
= 1/√2 – 1/√2
= 0
36) If the value of sin(θ + 300) is 3/√12, then what is the value of cos2 θ?
- 3/4
- 4/3
- 1/4
- None of the above
Answer: (a) 3/4
Explanation: Given sin (θ + 300) = 3/√12
It can be written as sin (θ + 300) = 3/2√3
Or, sin (θ + 300) = √3/2
=> sin (θ + 300) = sin 600
=> θ + 300 = 600
=> θ = 300
On putting θ = 300, in cos2 θ, we will get
cos2 300 = (√3/2)2
= 3/4
37) If the value of 4 cos2θ – 4√3 cos θ + 3 = 0, then what is the value of θ?
- 600
- 300
- 450
- None of the above
Answer: (b) 300
Explanation: In this example, we can find the value of θ by putting values given in options. It is the hit and trial approach. The value that satisfies the given equation will be considered as the value of θ.
Given 4 cos2θ – 4√3 cos θ + 3 = 0
So, in option A θ = 600 is given, let’s put it and see whether the equation will be satisfied or not –
4 cos2600 – 4√3 cos 600 + 3 = 0
4 x (1/2)2 – 4√3 x 1/2 + 3 = 0
=> 4/4 – 4/2√3 + 3 = 0
=> 4 – 4/2√3 = 0
=> 4(1 – 1/2√3) = 0 (will not satisfy the equation)
So, in option B, θ = 300 is given, let’s put it and see whether the equation will be satisfied or not –
4 cos2300 – 4√3 cos 300 + 3 = 0
4 x (√3 /2)2 – 4√3 x √3/2 + 3 = 0
=> 3 – 6 + 3 = 0
=> 6 – 6 = 0
=> 0 = 0 (Equation satisfied)
So, option B is correct, and the value of θ is 300.
38) Which of the following is the correct value of cos2 550 + cos2 350 + sin2 650 + sin2 250?
- 0
- 3
- 2
- None of the above
Answer: (c) 2
Explanation: cos2 550 + cos2 350 + sin2 650 + sin2 250
=> cos2 (900 – 350) + cos2 350 + sin2 650 + sin2 (900 – 650)
=> (sin2 350 + cos2 350) + (sin2 650 + cos2 650)
=> 1 + 1
= 2
39) If the value of tan 90 = p/q, then what is the value of sec2 810/ 1 + cot2 810?
- p2/q2
- 1
- q2/p2
- None of the above
Answer: (c) q2/p2
Explanation: sec2 810/ 1 + cot2 810
= sec2 810/ cosec2 810
= (1/cos2 810) / (1/sin2 810)
= sin2 810 / cos2 810
= tan2 810
= tan2 (900 – 90)
= cot2 90
= q2 / p2
40) If cot 450.sec 600 = A tan 300.sin 600, then which of the following is the correct value of A?
- 4
- 1
- √2
- None of the above
Answer: (a) 4
Explanation: Given cot 450.sec 600 = A tan 300.sin 600
So, 1 x 2 = A 1/√3 x √3/2
=> 2 = A/2
So, A = 4
41) If the value of sec2 θ + tan2 θ = 7, then what is the value of θ?
- 00
- 900
- 600
- 300
Answer: (c) 600
Explanation: Given sec2 θ + tan2 θ = 7
=> 1 + tan2 θ + tan2 θ = 7
=> 2tan2 θ + 1 = 7
=> 2tan2 θ = 6
=> tan2 θ = 3
=> tan θ = √3
Or θ = 600
We can also solve this question by using the hit and trial approach. We can directly check the values of θ given in options. The value that will satisfy the given condition will be the value of θ.
42) Which of the following is the correct value of (3 / 1+tan2 θ) + 2 sin2 θ + (1 / 1+cot2 θ)?
- 3
- 9
- 6
- None of the above
Answer: (a) 3
Explanation: (3 / 1+tan2 θ) + 2 sin2 θ + (1 / 1+cot2 θ) = ?
According to the trigonometric identities, the given equation can be written as –
= 3/sec2 θ + 2 sin2 θ + 1/cosec2 θ
= 3cos2 θ + 2 sin2 θ + sin2 θ
= 3cos2 θ + 3sin2 θ
= 3(cos2 θ + sin2 θ)
= 3
43) If the value of tan2 A = 1 + 2tan2 B, then what is the value of √2 cosA – cosB?
- 0
- 9
- √2
- √3
Answer: (a) 0
Explanation: Given tan2 A = 1 + 2tan2 B
=> sec2 A – 1 = 1 + 2 (sec2 B – 1)
=> sec2 A – 1 = 1 + 2 sec2 B – 2
=> sec2 A – 1 = 2 sec2 B – 1
=> 1/cos2 A = 2/cos2 B
=> cos2 B = 2cos2 A
=> or, cos B = √2 cos A
=> So, √2 cos A – cos B = 0
44) What will be the numerical value of (4 sec2 300 + cos2 600 – tan2 450) / (sin2 300 + cos2 300)?
- 55/12
- 45/12
- 1/12
- None of the above
Answer: (a) 55/12
Explanation: Given: (4 sec2 300 + cos2 600 – tan2 450) / (sin2 300 + cos2 300)
We have to put the numerical values,
= [4 (2/√3)2 + (½)2 – (1)2] / 1
=> sec2 A – 1 = 1 + 2 (sec2 B – 1)
=> sec2 A – 1 = 1 + 2 sec2 B – 2
=> sec2 A – 1 = 2 sec2 B – 1
=> 1/cos2 A = 2/cos2 B
=> cos2 B = 2cos2 A
=> or, cos B = √2 cos A
=> So, √2 cos A – cos B = 0
45) If the value of tan A = 2, then what is the value of (cosec2 A – sec2 A) / (cosec2 A + sec2 A)?
- 5/3
- 3/5
- – 5/3
- – 3/5
Answer: (d) – 3/5
Explanation: Given: tan A = 2
(cosec2 A – sec2 A) / (cosec2 A + sec2 A) = ?
On dividing above equation with cosec2 A, we will get –
= (1 – tan2 A) / (1 + tan2 A)
= (1 – 22) / (1 + 22) [because tan A = 2]
= – 3/5
46) Which of the following is the correct value of (5/sec2 θ) + 3 sin2 θ + (2 / 1+cot2 θ)?
- 3
- 9
- 5
- None of the above
Answer: (c) 5
Explanation: (5 / sec2 θ) + 3 sin2 θ + (2 / 1+cot2 θ) = ?
According to the trigonometric identities, the given equation can be written as –
= 5cos2 θ + 3 sin2 θ + 2/cosec2 θ
= 5cos2 θ + 3 sin2 θ + 2sin2 θ
= 5cos2 θ + 5sin2 θ
= 5(cos2 θ + sin2 θ)
= 5
47) Which of the following is the correct numerical value of 5 tan2 A – 5 sec2 A + 1?
- – 3
- 9
- 5
- – 4
Answer: (d) -4
Explanation: 5 tan2 A – 5 sec2 A + 1 = ?
= 5 (tan2 A – sec2 A) + 1
= 5 ((sin2 A/cos2 A) – (1/cos2 A)) + 1
= 5((sin2 A – 1) / cos2 A) + 1
= 5(- cos2 A / cos2 A) + 1
= – 5 + 1
= – 4
48) The value of cot 300/tan 600 is –
- 0
- 9
- 1
- – 2
Answer: (c) 1
Explanation: tan 600 = √3, cot 300 = √3
So, cot 300/tan 600 = √3 / √3
= 1
49) If the value of tanP + secP = a, then what is the value of cosP?
- 2a/a2 + 1
- a2 + 1/ 2a
- a2 – 1/ 2a
- None of the above
Answer: (a) 2a/a2 + 1
Explanation: It is given that, tanP + secP = a ……(i)
As we know, the trigonometric identity, sec2 P – tan2 P = 1 {we assume θ = P}
So, we can apply the formula a2 – b2 = (a – b) (a + b)
=> (sec P – tan P) (sec P + tan P) = 1
=> (sec P – tan P) x a = 1
=> sec P – tan P = 1/a …..(ii)
So, from equation (i) and (ii), we will get –
2sec P = a + 1/a
sec P = a2+1 / 2a
So, cos P = 2a / a2+1 [as sec P = 1/cosP]
50) Suppose cos θ + sin θ = √2 cos θ, then which of the following is the correct value of cos θ – sin θ?
- √2 cos θ
- √2 sin θ
- -√2 cos θ
- -√2 sin θ
Answer: (b) √2 sin θ
Explanation: It is given that, cos θ + sin θ = √2 cos θ …..(i)
On squaring both sides, we will get,
(cos θ + sin θ)2 = (√2 cos θ)2
=> cos2 θ + sin2 θ + 2 sin θ cos θ = 2 cos2 θ
Or, 2cos2 θ – cos2 θ – sin2 θ = 2 sinθ cosθ
=> cos2 θ – sin2 θ = 2 sin θ cos θ
=> (cos θ + sin θ) (cos θ – sin θ) = 2 sin θ cos θ
=> (√2 cos θ) (cos θ – sin θ) = 2 sin θ cos θ [from equation (i)]
=> (cos θ – sin θ) = 2 sinθ cosθ / √2 cos θ
= √2 sin θ