Usually, Trigonometry is used to deal with right-angled triangles. Trigonometry helps to find out the sides and angles using the relationship between them. Both the Sine and Cosine rules apply to any triangle - not just right-angled triangles.
Labelling[edit | edit source]
- In right angled triangles, the side next to the angle you are using is called the 'adjacent', the side opposite, is called that. The longest side is called the hypotenuse.
- For the sine rule, the cosine rule and areas of triangles, the sides are labelled a,b and c and the angles opposite a,b and c are labelled A, B and C.
Sine[edit | edit source]
Cosine[edit | edit source]
Tangent[edit | edit source]
Memory Aids[edit | edit source]
The sine, cosine, and tangents can be remembered by this rhyme: Some old hag came and had tea one afternoon (sine: opposite/hypotenuse, cosine: adjacent/hypotenuse, tangent: opposite/adjacent).
Another good memory aid is SOH, CAH, TOA. They are abbreviations for [sine=opposite/hypotenuse], [cos=adjacent/hypotenuse] and [tan=opposite/adjacent].
The Sine Rule[edit | edit source]
The Cosine Rule[edit | edit source]