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# When do you use sine rule and when cosine? watch

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1. How do you know when to use each rule???? thanks
2. there are various rules to learn... it is just as easy to start with the sine rule & switch over to the cosine rule if it doesn't work.
3. I will assume you know how to use them. In general, whenever you can. It simply depends on what information you have about a triangle, and what you what to find out. There can be moments where you could use either one, and it will be purely up to your preference which one you go for.
4. (Original post by mayjb)
How do you know when to use each rule???? thanks
Sine rule
use when you have 2 sides and an angle(1 exception which you use cosine rule instead)

Cosine rule
use when you have 2 adjacent sides and the included angle
5. Sine rule is used when you have two pairs of sides and angles where one value out of the two pairs is unknown. Note that only two pairs of the formula are used at any one time, not three.
Cosine rule is used when three sides and one angle is involved.
6. ok this makes sense, thank you!

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Updated: February 19, 2016
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