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Section E
USEFUL FORMULAE
Trigonometry
Formulae for the solution of
Formulae for the solution of
RIGHT ANGLED
OBLIQUE ANGLED
TRIANGLES
TRIANGLES
A
B
C
c
b
a
θ
A
B
C
c
a
b
Tan
θ
=
Sin
θ
=
Cos
θ
=
opposite
adjacent
opposite
hypotenuse
adjacent
hypotenuse
=
=
=
c
a
c
b
a
b
The Sine rule:
a
b c
Sin A
Sin B Sin C
The Cosine rule:
a² = b² + c² - 2bc Cos A
b² = a² + c² - 2ac Cos B
c² = a² + b² - 2ab Cos C
=
=
USEFUL VALUES IN TRIGNOMETRICALRATIOS
For right angled triangles
60°
30°
1
2
45°
45°
1
1
√
3
√
2
ANGLES 30° - 45° - 60°
θ
Tan
θ
Sin
θ
Cos
θ
30°
45°
60°
1
3
1
2
√
=0.577350
=0.500000
3
2
√
=0.866025
1
1
2
√
=0.707107
1
2
√
=0.707107
3 =1.732051
√
3
2
√
=0.866025
1
2 =0.500000
