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Thursday, 28 July 2022

Class 11 - Maths - Trigonometric Functions Notes, Solved Problems and NCERT Exercise 3.2 Solutions #eduvictors #class11Maths #Trigonometry

Class 11 - Maths - Trigonometric Functions Notes, Solved Problems and NCERT Exercise 3.2 Solutions

Class 11 - Maths - Trigonometric Functions Notes, Solved Problems and NCERT Exercise 3.2 Solutions #eduvictors #class11Maths #Trigonometry



Q1. What are quadrantal angles?

Answer: All angles which are integral multiples of π/2 are called quadrantal angles.

Therefore, for quadrantal angles, we have

cos 0° = 1,
sin 0° = 0,
cos π2 = 0 
sin π2 = 1
cos π = − 1 
sin π = 0
cos 3π2 = 0 
sin 3π2 = -1
cos 2π = 1 
sin 2π = 0

Trigonometric Functions

sin x = 0 implies x = nπ, where n is any integer
cos x = 0 implies x = (2n + 1) π2, where n is any integer

Other Trigonometric Functions are:

cosec x = 1sinx, x ≠ nπ, where n is an integer

sec x  = 1cosx, x ≠ (2n + 1)π2, where n is any integer

tan x = sinxcosx, x ≠ (2n + 1)π2, where n is any integer

cot x = cosxsinx, ≠ nπ, where n is any integer


Trignometry Identies:

sin²θ + cos²θ = 1

sec²θ - tan²θ = 1

cosec²θ - cot²θ = 1


 Trigonometric ratios of various angles:

Class 11 - Maths - Trigonometric Functions Notes, Solved Problems and NCERT Exercise 3.2 Solutions #eduvictors #class11Maths #Trigonometry

Class 11 - Maths - Trigonometric Functions Notes, Solved Problems and NCERT Exercise 3.2 Solutions #eduvictors #class11Maths #Trigonometry

(sin θ)(cosec θ) = 1, θ ≠ nπ, where n ∈ Z

(cos θ)(sec θ) = 1, θ ≠


Q2. Find the values of the other five trigonometric functions if , cos x = 12 lies in the third quadrant.

Answer:  cos x = 12

∴ sec x = 1cosx=112

∴ sec x = -2


Since, sin²θ + cos²θ = 1

∴ sin²x = 1 - cos²x 

sin²x = 1 - (12)2

sin²x = 1 - 14

sin²x = 34

sin x = ±32


Since x lies in the 3rd quadrant, the value of sin x will be negative

∴ sin x = -32

cosec x = 1sinx

cosex x = 132

cosec x = 23


tan x = sinxcosx

tan x = 3212

tan x = 3


cot x = 1tanx

cot x = 13



Q3. Find the values of the other five trigonometric functions if sin x = 35, x lies in the second quadrant.


Answer: sin x = 35 

cosec x = 1sinx=135

cosec x = 53 

Since, sin²x + cos²x = 1

cos²x  = 1 - sin²x 

cos²x  = 1 - (35)2

cos²x  = 1 - 925=1625

cos x = ±45

Since x lies in the 2nd quadrant, the value of cos x will be negative. 

∴ cos x = -45

sec x = 1cosx=54

tan x = sinxcosx=34

cot x = 1tanx=45


Q4. If sinθ=a42 then a lies in ?

Answer: Since -1 ≤ sin θ ≤ 1
Thus we have,
-1 ≤ a42 ≤ 1

⇒ -2 ≤ a - 4 ≤ 2

⇒ 2 ≤ a ≤ 6

⇒ a ∈ [2, 6]


Important points you should know:

(a) If A + B = 90° or 270°, then
(i) sin²A + sin²B = 1
(ii) cos²A + cos²B = 1
(iii) tan A . tan B = 1
(iv) cot A . cot B = 1

(b) If A + B = 180°, then
(i) cos A + cos B = 0
(ii) sin A - sin B = 0
(iii) tan A + tan B = 0

(c) If A + B = 360°, then
(i) sin A + sin B = 0
(ii) cos A - cos B = 0
(iii) tan A + tan B = 0


Q5. sin²35 + sin²55 =?

Answer: Since 35° + 55° = 90°
∴ sin²35 + sin²55 = 1



Q6. Find the value of the trigonometric function sin 765°

Answer: We know that the values of sin x repeat after an interval of 2π or 360°. 

∴ sin 765° = sin(2 × 360° + 45°) = sin 45° = 12


Q7. Find the value of the trigonometric function cosec(–1410°)

Answer: cosec(–1410°) = –cosec(1410°)

We know that the values of cosec x repeat after an interval of 2π or 360°.

∴ -cosec(-1410°) = -cosec (4 × 360° - 30°)
= cosec(30°)
= 2


Q8. Find the value of the trigonometric function tan19π3

Answer: We know that the values of tan x repeat after an interval of π or 180°

Given tan19π3=tan6π+π3

 = tanπ3

 = tan 60°

 = 3

 
👉See Also:

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