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.

## LabellingEdit

- 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.

## SineEdit

$ sin(x)=opposite/hypotenuse $

## CosineEdit

$ cos(x)=adjacent/hypotenuse $

## TangentEdit

$ tan(x)=opposite/adjacent $

## Memory AidsEdit

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 RuleEdit

## The Cosine RuleEdit

$ a^2=b^2 + c^2 -2bccos(A) $