1. ©G Dear2008 – Not to be sold/Free to use
General Mathematic
(HSC)
Further
Trigonometry
Cosine Rule
Sides
Stage 6 - Year 12
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©G Dear2008 – Not to be sold/Free to use

2. The Cosine Rule – Find a Side (1/2)b B
c2 = a2 + b2 – 2ab Cos C a C
b2 = a2 + c2 – 2ac Cos B
a2 = b2 + c2 – 2bc Cos A
To use the Cosine Rule – Area we need …
two sides and …
the angle between them.
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3. The Cosine Rule – Find a Side (2/2)
c2 = a2 + b2 – 2ab Cos C c 6
30o 7
c2 = 62
+ 72
– 2 x 6 x 7
x Cos 30
c = – 2 x 6 x 7 x Cos 30 =
≈ 3.5
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