Class 11 - Maths - Trigonometric Functions Notes, Solved Problems and NCERT Exercise 3.2 Solutions
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:
(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=1−12
∴ 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 = 1−√32
cosec x = 2√3
tan x = sinxcosx
tan x = √32−12
tan x = √3
cot x = 1tanx
cot x = 1√3
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=a−42 then a lies in ?
Answer: Since -1 ≤ sin θ ≤ 1
Thus we have,
-1 ≤ a−42 ≤ 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° = 1√2
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:
Ch2: Relations and Functions (1 Mark Q & A) Part-1
Ch2: Cartesian Product of Two Sets (Important Points)
Ch2: Relations - Domain, Range and Co-Domain (Solved Problems)
Ch3: Trigonometric Functions + NCERT Ex 3.1
Ch5: Complex Numbers (Part 1) - Solved Problems
Ch 13 Limits and Derivatives (Q & A ) Part -1
Ch2: Cartesian Product of Two Sets (Important Points)
Ch2: Relations - Domain, Range and Co-Domain (Solved Problems)
Ch3: Trigonometric Functions + NCERT Ex 3.1
Ch5: Complex Numbers (Part 1) - Solved Problems
Ch 13 Limits and Derivatives (Q & A ) Part -1
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