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Important Formulas & Examples: Trigonometric Functions - 1

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 Page 1


Trigonometric Formula Sheet
De?nition of the Trig Functions
Right Triangle De?nition
Assume that:
0 < ? <
? 2
or 0
 < ? < 90
 hypotenuse
adjacent
opposite
? sin? =
opp
hyp
csc? =
hyp
opp
cos? =
adj
hyp
sec? =
hyp
adj
tan? =
opp
adj
cot? =
adj
opp
Unit Circle De?nition
Assume ? can be any angle.
x
y
y
x
1
(x,y)
? sin? =
y
1
csc? =
1
y
cos? =
x
1
sec? =
1
x
tan? =
y
x
cot? =
x
y
Domains of the Trig Functions
sin? , 8 ? 2 (1 ,1 )
cos? , 8 ? 2 (1 ,1 )
tan? , 8 ? 6=
?
n+
1
2
?
? ,wheren2 Z
csc? , 8 ? 6= n? ,wheren2 Z
sec? , 8 ? 6=
?
n+
1
2
?
? ,wheren2 Z
cot? , 8 ? 6= n? ,wheren2 Z
Ranges of the Trig Functions
 1? sin? ? 1
 1? cos? ? 1
1? tan? ?1
csc?  1 and csc? ? 1
sec?  1 and sec? ? 1
1? cot? ?1
Periods of the Trig Functions
The period of a function is the number, T, such that f (? +T ) = f (? ).
So, if ! is a ?xed number and ? is any angle we have the following periods.
sin(!? ) ) T =
2? !
cos(!? ) ) T =
2? !
tan(!? ) ) T =
? !
csc(!? ) ) T =
2? !
sec(!? ) ) T =
2? !
cot(!? ) ) T =
? !
1
Page 2


Trigonometric Formula Sheet
De?nition of the Trig Functions
Right Triangle De?nition
Assume that:
0 < ? <
? 2
or 0
 < ? < 90
 hypotenuse
adjacent
opposite
? sin? =
opp
hyp
csc? =
hyp
opp
cos? =
adj
hyp
sec? =
hyp
adj
tan? =
opp
adj
cot? =
adj
opp
Unit Circle De?nition
Assume ? can be any angle.
x
y
y
x
1
(x,y)
? sin? =
y
1
csc? =
1
y
cos? =
x
1
sec? =
1
x
tan? =
y
x
cot? =
x
y
Domains of the Trig Functions
sin? , 8 ? 2 (1 ,1 )
cos? , 8 ? 2 (1 ,1 )
tan? , 8 ? 6=
?
n+
1
2
?
? ,wheren2 Z
csc? , 8 ? 6= n? ,wheren2 Z
sec? , 8 ? 6=
?
n+
1
2
?
? ,wheren2 Z
cot? , 8 ? 6= n? ,wheren2 Z
Ranges of the Trig Functions
 1? sin? ? 1
 1? cos? ? 1
1? tan? ?1
csc?  1 and csc? ? 1
sec?  1 and sec? ? 1
1? cot? ?1
Periods of the Trig Functions
The period of a function is the number, T, such that f (? +T ) = f (? ).
So, if ! is a ?xed number and ? is any angle we have the following periods.
sin(!? ) ) T =
2? !
cos(!? ) ) T =
2? !
tan(!? ) ) T =
? !
csc(!? ) ) T =
2? !
sec(!? ) ) T =
2? !
cot(!? ) ) T =
? !
1
Page 3


Trigonometric Formula Sheet
De?nition of the Trig Functions
Right Triangle De?nition
Assume that:
0 < ? <
? 2
or 0
 < ? < 90
 hypotenuse
adjacent
opposite
? sin? =
opp
hyp
csc? =
hyp
opp
cos? =
adj
hyp
sec? =
hyp
adj
tan? =
opp
adj
cot? =
adj
opp
Unit Circle De?nition
Assume ? can be any angle.
x
y
y
x
1
(x,y)
? sin? =
y
1
csc? =
1
y
cos? =
x
1
sec? =
1
x
tan? =
y
x
cot? =
x
y
Domains of the Trig Functions
sin? , 8 ? 2 (1 ,1 )
cos? , 8 ? 2 (1 ,1 )
tan? , 8 ? 6=
?
n+
1
2
?
? ,wheren2 Z
csc? , 8 ? 6= n? ,wheren2 Z
sec? , 8 ? 6=
?
n+
1
2
?
? ,wheren2 Z
cot? , 8 ? 6= n? ,wheren2 Z
Ranges of the Trig Functions
 1? sin? ? 1
 1? cos? ? 1
1? tan? ?1
csc?  1 and csc? ? 1
sec?  1 and sec? ? 1
1? cot? ?1
Periods of the Trig Functions
The period of a function is the number, T, such that f (? +T ) = f (? ).
So, if ! is a ?xed number and ? is any angle we have the following periods.
sin(!? ) ) T =
2? !
cos(!? ) ) T =
2? !
tan(!? ) ) T =
? !
csc(!? ) ) T =
2? !
sec(!? ) ) T =
2? !
cot(!? ) ) T =
? !
1
Identities and Formulas
Tangent and Cotangent Identities
tan? =
sin? cos? cot? =
cos? sin? Reciprocal Identities
sin? =
1
csc? csc? =
1
sin? cos? =
1
sec? sec? =
1
cos? tan? =
1
cot? cot? =
1
tan? Pythagorean Identities
sin
2
? +cos
2
? =1
tan
2
? +1=sec
2
? 1+cot
2
? =csc
2
? Even and Odd Formulas
sin( ? )= sin? cos( ? )=cos? tan( ? )= tan? csc( ? )= csc? sec( ? )=sec? cot( ? )= cot? Periodic Formulas
If n is an integer
sin(? +2? n) = sin? cos(? +2? n)=cos? tan(? +? n)=tan? csc(? +2? n)=csc? sec(? +2? n)=sec? cot(? +? n)=cot? Double Angle Formulas
sin(2? )=2sin? cos? cos(2? )=cos
2
?  sin
2
? =2cos
2
?  1
=1 2sin
2
? tan(2? )=
2tan? 1 tan
2
? Degrees to Radians Formulas
If x is an angle in degrees and t is an angle in
radians then:
? 180
 =
t
x
) t =
? x
180
 and x =
180
 t
? Half Angle Formulas
sin? =±
r
1 cos(2? )
2
cos? =±
r
1+cos(2? )
2
tan? =±
s
1 cos(2? )
1+cos(2? )
Sum and Di? erence Formulas
sin(? ± )=sin? cos ±cos? sin cos(? ± )=cos? cos ? sin? sin tan(? ± )=
tan? ±tan 1? tan? tan Product to Sum Formulas
sin? sin =
1
2
[cos(?   ) cos(? + )]
cos? cos =
1
2
[cos(?   )+cos(? + )]
sin? cos =
1
2
[sin(? + )+sin(?   )]
cos? sin =
1
2
[sin(? + ) sin(?   )]
Sum to Product Formulas
sin? +sin =2sin
?
? + 2
?
cos
?
?   2
?
sin?  sin =2cos
?
? + 2
?
sin
?
?   2
?
cos? +cos =2cos
?
? + 2
?
cos
?
?   2
?
cos?  cos = 2sin
?
? + 2
?
sin
?
?   2
?
Cofunction Formulas
sin
?
? 2
 ? ?
=cos? csc
?
? 2
 ? ?
=sec? tan
?
? 2
 ? ?
=cot? cos
?
? 2
 ? ?
=sin? sec
?
? 2
 ? ?
=csc? cot
?
? 2
 ? ?
=tan? 2
Page 4


Trigonometric Formula Sheet
De?nition of the Trig Functions
Right Triangle De?nition
Assume that:
0 < ? <
? 2
or 0
 < ? < 90
 hypotenuse
adjacent
opposite
? sin? =
opp
hyp
csc? =
hyp
opp
cos? =
adj
hyp
sec? =
hyp
adj
tan? =
opp
adj
cot? =
adj
opp
Unit Circle De?nition
Assume ? can be any angle.
x
y
y
x
1
(x,y)
? sin? =
y
1
csc? =
1
y
cos? =
x
1
sec? =
1
x
tan? =
y
x
cot? =
x
y
Domains of the Trig Functions
sin? , 8 ? 2 (1 ,1 )
cos? , 8 ? 2 (1 ,1 )
tan? , 8 ? 6=
?
n+
1
2
?
? ,wheren2 Z
csc? , 8 ? 6= n? ,wheren2 Z
sec? , 8 ? 6=
?
n+
1
2
?
? ,wheren2 Z
cot? , 8 ? 6= n? ,wheren2 Z
Ranges of the Trig Functions
 1? sin? ? 1
 1? cos? ? 1
1? tan? ?1
csc?  1 and csc? ? 1
sec?  1 and sec? ? 1
1? cot? ?1
Periods of the Trig Functions
The period of a function is the number, T, such that f (? +T ) = f (? ).
So, if ! is a ?xed number and ? is any angle we have the following periods.
sin(!? ) ) T =
2? !
cos(!? ) ) T =
2? !
tan(!? ) ) T =
? !
csc(!? ) ) T =
2? !
sec(!? ) ) T =
2? !
cot(!? ) ) T =
? !
1
Identities and Formulas
Tangent and Cotangent Identities
tan? =
sin? cos? cot? =
cos? sin? Reciprocal Identities
sin? =
1
csc? csc? =
1
sin? cos? =
1
sec? sec? =
1
cos? tan? =
1
cot? cot? =
1
tan? Pythagorean Identities
sin
2
? +cos
2
? =1
tan
2
? +1=sec
2
? 1+cot
2
? =csc
2
? Even and Odd Formulas
sin( ? )= sin? cos( ? )=cos? tan( ? )= tan? csc( ? )= csc? sec( ? )=sec? cot( ? )= cot? Periodic Formulas
If n is an integer
sin(? +2? n) = sin? cos(? +2? n)=cos? tan(? +? n)=tan? csc(? +2? n)=csc? sec(? +2? n)=sec? cot(? +? n)=cot? Double Angle Formulas
sin(2? )=2sin? cos? cos(2? )=cos
2
?  sin
2
? =2cos
2
?  1
=1 2sin
2
? tan(2? )=
2tan? 1 tan
2
? Degrees to Radians Formulas
If x is an angle in degrees and t is an angle in
radians then:
? 180
 =
t
x
) t =
? x
180
 and x =
180
 t
? Half Angle Formulas
sin? =±
r
1 cos(2? )
2
cos? =±
r
1+cos(2? )
2
tan? =±
s
1 cos(2? )
1+cos(2? )
Sum and Di? erence Formulas
sin(? ± )=sin? cos ±cos? sin cos(? ± )=cos? cos ? sin? sin tan(? ± )=
tan? ±tan 1? tan? tan Product to Sum Formulas
sin? sin =
1
2
[cos(?   ) cos(? + )]
cos? cos =
1
2
[cos(?   )+cos(? + )]
sin? cos =
1
2
[sin(? + )+sin(?   )]
cos? sin =
1
2
[sin(? + ) sin(?   )]
Sum to Product Formulas
sin? +sin =2sin
?
? + 2
?
cos
?
?   2
?
sin?  sin =2cos
?
? + 2
?
sin
?
?   2
?
cos? +cos =2cos
?
? + 2
?
cos
?
?   2
?
cos?  cos = 2sin
?
? + 2
?
sin
?
?   2
?
Cofunction Formulas
sin
?
? 2
 ? ?
=cos? csc
?
? 2
 ? ?
=sec? tan
?
? 2
 ? ?
=cot? cos
?
? 2
 ? ?
=sin? sec
?
? 2
 ? ?
=csc? cot
?
? 2
 ? ?
=tan? 2
Unit Circle
0
 ,2? (1,0)
180
 ,? ( 1,0)
(0,1)
90
 ,
? 2
(0, 1)
270
 ,
3? 2
30
 ,
? 6
(
p 3
2
,
1
2
)
45
 ,
? 4
(
p 2
2
,
p 2
2
)
60
 ,
? 3
(
1
2
,
p 3
2
)
120
 ,
2? 3
( 1
2
,
p 3
2
)
135
 ,
3? 4
( p 2
2
,
p 2
2
)
150
 ,
5? 6
( p 3
2
,
1
2
)
210
 ,
7? 6
( p 3
2
, 1
2
)
225
 ,
5? 4
( p 2
2
, p 2
2
)
240
 ,
4? 3
( 1
2
, p 3
2
)
300
 ,
5? 3
(
1
2
, p 3
2
)
315
 ,
7? 4
(
p 2
2
, p 2
2
)
330
 ,
11? 6
(
p 3
2
, 1
2
)
For any ordered pair on the unit circle (x,y):cos? = x and sin? = y
Example
cos(
7? 6
)= p 3
2
sin(
7? 6
)= 1
2
3
Page 5


Trigonometric Formula Sheet
De?nition of the Trig Functions
Right Triangle De?nition
Assume that:
0 < ? <
? 2
or 0
 < ? < 90
 hypotenuse
adjacent
opposite
? sin? =
opp
hyp
csc? =
hyp
opp
cos? =
adj
hyp
sec? =
hyp
adj
tan? =
opp
adj
cot? =
adj
opp
Unit Circle De?nition
Assume ? can be any angle.
x
y
y
x
1
(x,y)
? sin? =
y
1
csc? =
1
y
cos? =
x
1
sec? =
1
x
tan? =
y
x
cot? =
x
y
Domains of the Trig Functions
sin? , 8 ? 2 (1 ,1 )
cos? , 8 ? 2 (1 ,1 )
tan? , 8 ? 6=
?
n+
1
2
?
? ,wheren2 Z
csc? , 8 ? 6= n? ,wheren2 Z
sec? , 8 ? 6=
?
n+
1
2
?
? ,wheren2 Z
cot? , 8 ? 6= n? ,wheren2 Z
Ranges of the Trig Functions
 1? sin? ? 1
 1? cos? ? 1
1? tan? ?1
csc?  1 and csc? ? 1
sec?  1 and sec? ? 1
1? cot? ?1
Periods of the Trig Functions
The period of a function is the number, T, such that f (? +T ) = f (? ).
So, if ! is a ?xed number and ? is any angle we have the following periods.
sin(!? ) ) T =
2? !
cos(!? ) ) T =
2? !
tan(!? ) ) T =
? !
csc(!? ) ) T =
2? !
sec(!? ) ) T =
2? !
cot(!? ) ) T =
? !
1
Identities and Formulas
Tangent and Cotangent Identities
tan? =
sin? cos? cot? =
cos? sin? Reciprocal Identities
sin? =
1
csc? csc? =
1
sin? cos? =
1
sec? sec? =
1
cos? tan? =
1
cot? cot? =
1
tan? Pythagorean Identities
sin
2
? +cos
2
? =1
tan
2
? +1=sec
2
? 1+cot
2
? =csc
2
? Even and Odd Formulas
sin( ? )= sin? cos( ? )=cos? tan( ? )= tan? csc( ? )= csc? sec( ? )=sec? cot( ? )= cot? Periodic Formulas
If n is an integer
sin(? +2? n) = sin? cos(? +2? n)=cos? tan(? +? n)=tan? csc(? +2? n)=csc? sec(? +2? n)=sec? cot(? +? n)=cot? Double Angle Formulas
sin(2? )=2sin? cos? cos(2? )=cos
2
?  sin
2
? =2cos
2
?  1
=1 2sin
2
? tan(2? )=
2tan? 1 tan
2
? Degrees to Radians Formulas
If x is an angle in degrees and t is an angle in
radians then:
? 180
 =
t
x
) t =
? x
180
 and x =
180
 t
? Half Angle Formulas
sin? =±
r
1 cos(2? )
2
cos? =±
r
1+cos(2? )
2
tan? =±
s
1 cos(2? )
1+cos(2? )
Sum and Di? erence Formulas
sin(? ± )=sin? cos ±cos? sin cos(? ± )=cos? cos ? sin? sin tan(? ± )=
tan? ±tan 1? tan? tan Product to Sum Formulas
sin? sin =
1
2
[cos(?   ) cos(? + )]
cos? cos =
1
2
[cos(?   )+cos(? + )]
sin? cos =
1
2
[sin(? + )+sin(?   )]
cos? sin =
1
2
[sin(? + ) sin(?   )]
Sum to Product Formulas
sin? +sin =2sin
?
? + 2
?
cos
?
?   2
?
sin?  sin =2cos
?
? + 2
?
sin
?
?   2
?
cos? +cos =2cos
?
? + 2
?
cos
?
?   2
?
cos?  cos = 2sin
?
? + 2
?
sin
?
?   2
?
Cofunction Formulas
sin
?
? 2
 ? ?
=cos? csc
?
? 2
 ? ?
=sec? tan
?
? 2
 ? ?
=cot? cos
?
? 2
 ? ?
=sin? sec
?
? 2
 ? ?
=csc? cot
?
? 2
 ? ?
=tan? 2
Unit Circle
0
 ,2? (1,0)
180
 ,? ( 1,0)
(0,1)
90
 ,
? 2
(0, 1)
270
 ,
3? 2
30
 ,
? 6
(
p 3
2
,
1
2
)
45
 ,
? 4
(
p 2
2
,
p 2
2
)
60
 ,
? 3
(
1
2
,
p 3
2
)
120
 ,
2? 3
( 1
2
,
p 3
2
)
135
 ,
3? 4
( p 2
2
,
p 2
2
)
150
 ,
5? 6
( p 3
2
,
1
2
)
210
 ,
7? 6
( p 3
2
, 1
2
)
225
 ,
5? 4
( p 2
2
, p 2
2
)
240
 ,
4? 3
( 1
2
, p 3
2
)
300
 ,
5? 3
(
1
2
, p 3
2
)
315
 ,
7? 4
(
p 2
2
, p 2
2
)
330
 ,
11? 6
(
p 3
2
, 1
2
)
For any ordered pair on the unit circle (x,y):cos? = x and sin? = y
Example
cos(
7? 6
)= p 3
2
sin(
7? 6
)= 1
2
3
Read More

FAQs on Important Formulas & Examples: Trigonometric Functions - 1

1. What are the six trigonometric ratios and how do I remember them easily for CBSE exams?
Ans. The six trigonometric ratios are sine, cosine, tangent, cosecant, secant, and cotangent. Students often use the mnemonic SOH-CAH-TOA to remember sine (opposite/hypotenuse), cosine (adjacent/hypotenuse), and tangent (opposite/adjacent). The reciprocal functions-cosecant, secant, and cotangent-are simply 1/sin, 1/cos, and 1/tan respectively. Flashcards and mind maps help reinforce these relationships quickly before exams.
2. Why do trigonometric functions have different values at 0°, 30°, 45°, 60°, and 90°?
Ans. These special angles produce exact trigonometric values based on specific right-angled triangle ratios. At 0°, sine equals 0 and cosine equals 1; at 90°, sine equals 1 and cosine equals 0. The 30-60-90 and 45-45-90 triangles generate predictable ratios like √3/2 and 1/√2 that appear repeatedly in problems. Understanding this pattern prevents calculation errors in Grade 12 mathematics.
3. How do I know which trigonometric function to use when solving a right triangle problem?
Ans. Identify which sides you know and which you need to find. If you have the opposite side and hypotenuse, use sine; for adjacent and hypotenuse, use cosine; for opposite and adjacent, use tangent. This selection method-matching available information to the correct trigonometric ratio-is essential for Grade 12 problem-solving and ensures you don't waste time trying wrong approaches during board exams.
4. What's the difference between sin²θ + cos²θ = 1 and other trigonometric identities?
Ans. The Pythagorean identity sin²θ + cos²θ = 1 is fundamental-it applies to all angles and forms the basis for deriving other identities like 1 + tan²θ = sec²θ. Other identities are specific to angle relationships, reciprocals, or sum-difference formulas. Mastering this core identity unlocks simplification of complex trigonometric expressions, which frequently appears in CBSE Class 12 examinations.
5. Can trigonometric function values be negative, and when does this happen?
Ans. Yes, trigonometric function values are negative in specific quadrants. Sine is negative in the third and fourth quadrants; cosine is negative in the second and third quadrants; tangent is negative in the second and fourth quadrants. The ASTC rule (All-Students-Take-Calculus) helps track this. Understanding sign changes across quadrants prevents critical mistakes in evaluating trigonometric expressions and angle-based calculations.
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