Sine and Cosine Formulae
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Sine and Cosine Formulae
sin x = sin (180 - x)
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
which 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).

© Matthew Pinkey

Other Notes in this Category

1. Double angle formulae
2. Pythagorean Identities
3. Radians
4. Sec, cosec, cot
5. Sin, Cos, Tan
6. Sine and Cosine Formulae
7. Solving Trigonometric Equations

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