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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).