# sine and cosine rule

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• Created by: iammoshi
• Created on: 29-05-16 11:46
The sine rule
a/sinA = b/sinB = c/sinC
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The first cosine rule
a^2 = b^2 + c^2 - 2bc cosA
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The second cosine rule
cosA = (b^2 + c^2 - a^2)/ 2bc
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When to use the sine rule
There are 2 cases. 1. Two sides and an angle opposite to one of the two sides. 2. One side and any two angles.
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When to use the first cosine rule
When there is two sides and an angle enclosed between the two sides
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When to use the second cosine rule
When you are given a triangle with all 3 sides and no angles
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Remember
you only use these rules when a triangle is NOT right angle, you can use normal trig for that
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Use this website
you can find all of this at http://www.cimt.plymouth.ac.uk/projects/mepres/step-up/sect4/index.htm. It includes worked answers and questions you can try yourself
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## Other cards in this set

### Card 2

#### Front

a^2 = b^2 + c^2 - 2bc cosA

#### Back

The first cosine rule

### Card 3

#### Front

cosA = (b^2 + c^2 - a^2)/ 2bc

### Card 4

#### Front

There are 2 cases. 1. Two sides and an angle opposite to one of the two sides. 2. One side and any two angles.

### Card 5

#### Front

When there is two sides and an angle enclosed between the two sides