Trigonometric Identities
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x
yrθ
sin
cos
tan
x
ry
rx
y
sin
cos
tan (cos 0)
x y
r rx r
r y
x
y
2 2 2 2
2
2
2
1
x y x y
r r r
r
r
TOA
CAH
SOH
Pythagoras Theorem:2 2 2r x y
2 2sin cos 1x x

Definitions:
sin
cos
tan
opp
hyp
adj
hyp
opp
adj
TOA
CAH
SOH1
cosecsin
1sec
cos
1cot
tan
Reciprocal

Trigonometric identities2 2sin cos 1x x
xx
x
x
xx
22
2
2
22
cos
1
cos
cos
cos
sin:cos
2 2tan 1 secx x
xx
x
x
xx
22
2
2
22
sin
1
sin
cos
sin
sin:sin
2 21 cot cosecx x

1 1 1cosec , sec , cot
sin cos tan
(1) Reciprocals2 2
2 2
2 2
sin cos 1
tan 1 sec
1 cot cosec
(2) Shaded Triangles
sin cos cottan , sin , cos ,...
cos cot cosecetc
(3) Clockwise direction
cos sin tancot , cos , sin ,...
sin tan secetc
(4) Anti-clockwise direction

Find the angles between 0 and 360 which satisfy:
sec x = 2
sec x = 2
2
1cos
2cos
1
x
x
x = 60 or 360 − 60 = 300
B.A = 60, 1st/4th Quad

Find the angles between 0 and 360 which satisfy:
010sec23sec5 2 xx
x = 78.5 or 281.5
05sec2sec5 xx 5secor5
2sec xx
5
1cosor
2
5cos xx
54.28146.78360or 46.78 xx
(reject)
Factorise like quadratic
B.A = 78.46, 1st/4th Quad

Given that A is obtuse and cot A 3 , find the exact value of
secA cosecA
1cot 3 tan
3A A 1. Change to basic trigo function
2. Draw ∆, use pythagoras1
3
10
1sec
cos
10
3
AA
3. Find basic trigo function
1cosec
sin
10
AA
AS
T C

cot A cosecA
1cot
tan1
2
AA
2
1
5
1cos
5
5
5
A
1cosec
sin12
5
5
2
AA
2tan A Atan cos AGiven that and that and have opposite signs, find the value of
cos A
AS
T C

Solve the following equations for 0 360o o x
2. Find the new range
sec( ) x 2
o o360 0x
3. Find B.A
1cos( )
2x 1. Change to basic trigo function
1 1cos 60
2BA
60 , 300x
4. Find the quadrants using ASTC
60 ,300x
5. Solve unknown in ( )
6. Solve x

Solve the following equations for 0 360o o x
cot 2sin 25x
2. Find B.A
1tan
2sin 25x 1. Change to basic trigo function
1 1. tan 49.79
2sin 25B A
49.8 ,229.8x
3. Find the quadrants using ASTCAS
T C

Solve the following equations for 0 360o o x
sec 2cosx x
2
2
sec 2cos
12cos
cos
2cos 1
1cos
2
x x
xx
x
x
45 ,135 ,225 ,315x
1 1. cos 45
2B A

2sin 3x 2cos 1y
4)1()3( 22 yx
Given that and , show that
For “showing” questions, always start from one side and end with the other
2 2
2 2
2 2
2 2
2 2
( 3) ( 1)
( 3) ( 1)
4sin 4cos
4(sin cos )
4 ( sin cos 1
2si 2c
)
osn 3 1
LHS x y

0sin2cos5 xx
0 360x
2sin 5cosx xsin 5
cos 2
x
x
5tan
2x
1 5. tan 68.198...
2B A
111.8 ,291.8x
2nd/4th Quad
AS
T C

22 tan 4 secx x
0 360x
22 tan 4 ( 1)tanx x
tan 3 tan 1x or x
. 71.565 45B A or
45 ,225 ,108.4 ,288.4x
AS
T C
2tan 2 tan 3 0x x (tan 3)(tan 1) 0x x
2nd/4th 1st /3rd

3sin 2 2 0x
0 360x
2sin 2
3x
. 41.81B A
221.8 ,318.2 ,581.8 ,678.22x
AS
T C
3rd /4th
0 2 720x
110.9 ,159.1 ,290.9 ,339.1x

2sin tany y0 360x
180 ,60 ,300y
sin2sin
cos
yy
y
2sin cos sin 0
sin (2cos 1) 0
1sin 0 cos
2
y y y
y y
y or y
1st /4thAll
. 0 60B A or

2cos 2 1 2x
0 360x
2 78.05 ,281.95 ,438.05 ,641.95
39.0 ,141.0 ,219.0 ,321.0
x
x
2 1cos 2
2x
1st /4th
. 78.05B A
0 2 720x

2(cos 2)(cos 1) sinx x x
0 360x
180x
2 2cos cos 2 1 cosx x x
2nd /3rd
. 90B A
22cos cos 3 0x x (2cos 3)(cos 1) 0x x
3cos ( ) cos 1
2x rej or x

2 22sin 5sin cos 3cosx x x x
0 360x
71.6 ,251.6 ,153.4 ,333.4x
2 22sin 5sin cos 3cos 0x x x x
. 26.565 71.565B A or
(2sin cos )(sin 3cos ) 0x x x x
2sin cos 0 sin 3cos 0x x or x x
2sin cos sin 3cos
1tan tan 3
2
x x or x x
x or x
1st /3rd 2nd / 4th

10sec5tan2 2
tanIf is obtuse and
, find the value of without using a calculator.
22(sec 1) 5sec 10 22sec 5sec 12 0
(2sec 3)(sec 4) 0 3
sec sec 42or
1cos ( is ob
2c tuo
4s se)
3reor j
3
2
55
tan2