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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