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Revision Notes: Trigonometric Function

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 Page 1


 
KEY POINTS
? A radian is an angle subtended at the centre of a circle by an arc whose 
length is equal to the radius of the circle. We denote 1 radian by 1
c
. 
? ? radian = 180 degree, 1° = 60’
1 radian = 
180
?
degree and 1’ = 60’ ’ 
1 degree = 
180
?
radian
? If an arc of length l makes an angle qradian at the centre of a circle of 
radius r, we have 
l
r
? ?
Page 2


 
KEY POINTS
? A radian is an angle subtended at the centre of a circle by an arc whose 
length is equal to the radius of the circle. We denote 1 radian by 1
c
. 
? ? radian = 180 degree, 1° = 60’
1 radian = 
180
?
degree and 1’ = 60’ ’ 
1 degree = 
180
?
radian
? If an arc of length l makes an angle qradian at the centre of a circle of 
radius r, we have 
l
r
? ?
 
Some Standard Results 
?
 
ta n ta n
ta n(x + y)
1 ta n .ta n
x y
x y
?
?
?
Page 3


 
KEY POINTS
? A radian is an angle subtended at the centre of a circle by an arc whose 
length is equal to the radius of the circle. We denote 1 radian by 1
c
. 
? ? radian = 180 degree, 1° = 60’
1 radian = 
180
?
degree and 1’ = 60’ ’ 
1 degree = 
180
?
radian
? If an arc of length l makes an angle qradian at the centre of a circle of 
radius r, we have 
l
r
? ?
 
Some Standard Results 
?
 
ta n ta n
ta n(x + y)
1 ta n .ta n
x y
x y
?
?
?
 
cot(x +y) = 
cot x.cot y-1
coty + cotx
? sin (x - y) = sinx.cosy - cosx siny 
cos (x - y) = cosx cosy + sinxsiny 
ta n ta n
ta n(x-y)
1 ta n .ta n
x y
x y
?
?
?
cot .cot 1
cot(x-y) 
cot cot
x y
y x
?
?
?
? tan(x +y + z) = 
ta n ta n ta n ta n ta n ta n
1 ta n ta n ta n .ta n ta n ta n
x y z x y z
x y y z z x
? ? ?
? ? ?
? 2sinx cosy = sin(x + y) + sin(x - y) 
2cosx siny = sin(x + y) - sin(x - y) 
2cosx cosy = cos (x + y) + cos (x -y) 
2sinx siny = cos (x + y) - cos (x + y) 
? sin x + sin y = 2 sin 
x y											 ?
 cos 
x y ?
cos x +cos y = 2 cos
2
x y ?
 cos 
2
x y ?
?
?
?
?
Page 4


 
KEY POINTS
? A radian is an angle subtended at the centre of a circle by an arc whose 
length is equal to the radius of the circle. We denote 1 radian by 1
c
. 
? ? radian = 180 degree, 1° = 60’
1 radian = 
180
?
degree and 1’ = 60’ ’ 
1 degree = 
180
?
radian
? If an arc of length l makes an angle qradian at the centre of a circle of 
radius r, we have 
l
r
? ?
 
Some Standard Results 
?
 
ta n ta n
ta n(x + y)
1 ta n .ta n
x y
x y
?
?
?
 
cot(x +y) = 
cot x.cot y-1
coty + cotx
? sin (x - y) = sinx.cosy - cosx siny 
cos (x - y) = cosx cosy + sinxsiny 
ta n ta n
ta n(x-y)
1 ta n .ta n
x y
x y
?
?
?
cot .cot 1
cot(x-y) 
cot cot
x y
y x
?
?
?
? tan(x +y + z) = 
ta n ta n ta n ta n ta n ta n
1 ta n ta n ta n .ta n ta n ta n
x y z x y z
x y y z z x
? ? ?
? ? ?
? 2sinx cosy = sin(x + y) + sin(x - y) 
2cosx siny = sin(x + y) - sin(x - y) 
2cosx cosy = cos (x + y) + cos (x -y) 
2sinx siny = cos (x + y) - cos (x + y) 
? sin x + sin y = 2 sin 
x y											 ?
 cos 
x y ?
cos x +cos y = 2 cos
2
x y ?
 cos 
2
x y ?
?
?
?
?
 
? sin 2x = 2 sin x cos x =
2
2 tan
1 tan
x
x ?
?
2
2
1 ta n
1 ta n
x
x
?
?
? tan 2x =
2
2 tan
1 tan
x
x ?
? tan 3x  = 
3
2
3ta n ta n
1 3ta n
x x
x
?
?
? sin(x + y) sin(x — y) = sin x — sin y= cos y — cos x 
?
? General	solution	—	A	solution	of	a	trigonometric	equation,	generalised	by	means	of	
periodicity,	is	known	as	the	general	solution.	Principal	solutions	—	The	solutions	
of	a	trigonometric	equation	which 
lie in [0,2 ?) are called its principal solutions. 
? sin ? = 0 ? ? ?? = n ? ? ? where ? n ? ? z 
? cos ? = 0 ? ? ? ? = (2n ? ? ?
2
?
, where n ? ? z
? tan ? = 0 ? ? ?? = n ? ? ? where ? n ? ? z 
? sin ? = sin ? ? ? ? ? = n ? ? ?(— 1)
n
? ? where n ? z 
? cos ? = cos ? ? ? ? ?? = 2n ? ? ? ? ? ? where n ? ? z 
? tan ? = tan ? ? ? ? ?? = n ? ? ? ? ? ? where n ? ? z 
?
?
Page 5


 
KEY POINTS
? A radian is an angle subtended at the centre of a circle by an arc whose 
length is equal to the radius of the circle. We denote 1 radian by 1
c
. 
? ? radian = 180 degree, 1° = 60’
1 radian = 
180
?
degree and 1’ = 60’ ’ 
1 degree = 
180
?
radian
? If an arc of length l makes an angle qradian at the centre of a circle of 
radius r, we have 
l
r
? ?
 
Some Standard Results 
?
 
ta n ta n
ta n(x + y)
1 ta n .ta n
x y
x y
?
?
?
 
cot(x +y) = 
cot x.cot y-1
coty + cotx
? sin (x - y) = sinx.cosy - cosx siny 
cos (x - y) = cosx cosy + sinxsiny 
ta n ta n
ta n(x-y)
1 ta n .ta n
x y
x y
?
?
?
cot .cot 1
cot(x-y) 
cot cot
x y
y x
?
?
?
? tan(x +y + z) = 
ta n ta n ta n ta n ta n ta n
1 ta n ta n ta n .ta n ta n ta n
x y z x y z
x y y z z x
? ? ?
? ? ?
? 2sinx cosy = sin(x + y) + sin(x - y) 
2cosx siny = sin(x + y) - sin(x - y) 
2cosx cosy = cos (x + y) + cos (x -y) 
2sinx siny = cos (x + y) - cos (x + y) 
? sin x + sin y = 2 sin 
x y											 ?
 cos 
x y ?
cos x +cos y = 2 cos
2
x y ?
 cos 
2
x y ?
?
?
?
?
 
? sin 2x = 2 sin x cos x =
2
2 tan
1 tan
x
x ?
?
2
2
1 ta n
1 ta n
x
x
?
?
? tan 2x =
2
2 tan
1 tan
x
x ?
? tan 3x  = 
3
2
3ta n ta n
1 3ta n
x x
x
?
?
? sin(x + y) sin(x — y) = sin x — sin y= cos y — cos x 
?
? General	solution	—	A	solution	of	a	trigonometric	equation,	generalised	by	means	of	
periodicity,	is	known	as	the	general	solution.	Principal	solutions	—	The	solutions	
of	a	trigonometric	equation	which 
lie in [0,2 ?) are called its principal solutions. 
? sin ? = 0 ? ? ?? = n ? ? ? where ? n ? ? z 
? cos ? = 0 ? ? ? ? = (2n ? ? ?
2
?
, where n ? ? z
? tan ? = 0 ? ? ?? = n ? ? ? where ? n ? ? z 
? sin ? = sin ? ? ? ? ? = n ? ? ?(— 1)
n
? ? where n ? z 
? cos ? = cos ? ? ? ? ?? = 2n ? ? ? ? ? ? where n ? ? z 
? tan ? = tan ? ? ? ? ?? = n ? ? ? ? ? ? where n ? ? z 
?
?
 
5 1
sin18
4
?
? ? ;  
10 2 5
cos18
4
?
? ?
10 2 5 5 1
sin36 ; cos36
4 4
? ?
? ? ? ?
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FAQs on Revision Notes: Trigonometric Function

1. What are the key trigonometric ratios and how do they relate to a right triangle?
Ans. The six main trigonometric ratios-sine, cosine, tangent, cotangent, secant, and cosecant-describe relationships between angles and sides in right triangles. Sine equals opposite over hypotenuse, cosine equals adjacent over hypotenuse, and tangent equals opposite over adjacent. These fundamental ratios form the foundation for solving angle and side problems in JEE Main & Advanced examinations. Students should memorise SOHCAHTOA as a quick recall method for primary trigonometric functions.
2. How do I remember all the trigonometric identities for JEE exams?
Ans. Trigonometric identities fall into key categories: reciprocal identities (like sin²θ + cos²θ = 1), quotient identities (tanθ = sinθ/cosθ), and co-function identities (sin(90°-θ) = cosθ). Rather than memorising each separately, understand that all derive from the Pythagorean identity. Refer to mind maps and flashcards that visually organise these relationships, making pattern recognition easier during high-pressure JEE problem-solving.
3. Why do trigonometric values repeat, and what's the period of sine and cosine?
Ans. Trigonometric functions are periodic because they describe rotational angles on the unit circle. Both sine and cosine repeat every 2π radians (360°), making their period 2π. Tangent repeats every π radians (180°) since it depends on the ratio of sine to cosine. Understanding periodicity helps solve trigonometric equations efficiently and predict function behaviour across multiple cycles on JEE question papers.
4. What's the difference between radians and degrees, and when should I use each?
Ans. Degrees divide a circle into 360 equal parts; radians measure angles using arc length relative to radius (2π radians = 360°). JEE Advanced typically uses radians for calculus-based problems and theoretical questions, while degrees appear in geometry and practical applications. Converting between them uses the formula: radians = degrees × (π/180). Mastering both units prevents calculation errors in mixed-format examination problems.
5. How can I quickly identify which trigonometric formula to apply when solving complex JEE problems?
Ans. Recognise problem patterns: sum-to-product formulas simplify additions like sinA + sinB, product-to-sum formulas handle products like sinA·sinB, and double-angle formulas (sin2θ = 2sinθcosθ) reduce higher multiples. Strategy involves examining the given expression's structure and matching it to a relevant trigonometric identity. Practising varied question types through worksheets and MCQ tests on EduRev builds pattern recognition speed essential for time-bound JEE Main examinations.
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