sin x = sin (180 – x)

e.g. sin 130 = sin (180 – 130) = sin 50

cos x = -cos (180 – x)

*The Sine Rule:*

This works in any triangle:

__ a __ = __ b __ = __ c __

sinA sinB sinC

alternatively, __sinA__ = __sinB__ = __sinC__

a b c

NOTE: the triangle is labelled as follows:

*The Cosine Rule*:

c² = a² + b² – 2abcosC

can also be written as:

a² = b² + c² – 2bccosA

This also works in any triangle.

**The area of a triangle**

The area of any triangle is ½ absinC (using the above notation)

This formula is useful if you don’t know the height of a triangle (since you need to know the height for ½ base × height).