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### Sine rule

The **sine rule** is

##### Explanation

In triangle ABC, you can describe the sine of any angle easily using the altitudes.

With the altitude from angle C we find

and

It follows that

and you can write this as

Now we take the altitude from angle B, and find

and

It follows that

and you can write this as

Now we take the altitude from angle A, and find

and

It follows that

and you can write it as

All this gives