# The Cosine Rule A B C a b c. The Cosine Rule A B C a b c.

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The Cosine Rule A B C a b c

The Cosine Rule A B C a b c

A B C a b c

When To Use The Cosine Rule. The Cosine Rule can be used to find a third side of a triangle if you have the other two sides and the angle between them. 6 10 65 o L89 o 13.8 6.2 W 147 o 8 11 M

Calculating Sides Using The Cosine Rule(1). Calculate the length AC 30m 55° 40m

30m 55° 40m b a c

Calculating Sides Using The Cosine Rule(2). Calculate the length CB 100 ° 13cm 5cm

100 ° 13cm 5cm b a c

Rearranging the cosine rule. You now have a formula for finding an angle if you know all three sides of the triangle.

Calculating Angles Using The Cosine Rule (1). Calculate the angle CAB

b a c ?

Calculating Angles Using The Cosine Rule (2). Calculate the angle ?

B A C b a c

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