The Sine Rule
The sine rule is an important rule relating the sides and angles of
any triangle (it doesn't have to be right-angled!):
If a, b and c are the lengths of the sides opposite the angles A, B and C in
a triangle, then:
If you wanted to find an angle, you can write this as:
The Cosine Rule
This also works in any triangle:
c² = a² + b² - 2abcosC
which can also be written as:
a² = b² + c² -
The area of a triangle
The area of any triangle is ½ absinC (using the above notation).
formula is useful if you don't know the height of a triangle (since you need to
know the height for ½ base × height).
Copyright © Matthew Pinkney 2003