cosine and sine rules? (1 Viewer)

[orly?]

what's the difference between these two rules?

sin rule is
a/sinA = b/sinB etc.

 

[DownInFlames]

cosine rule:

A^2 = B^2 + C^2 - BCcosA


cosA = (B^2 + C^2- A^2)/BC

 

[Iruka]

Which rule you use depends on what information you have been given. For example, if you have been given the length of three sides of a triangle and are trying to find the size of an angle, you would use the cosine rule - in this case the sine rule wont help you.

In some cases, you can use either rule. In general, the sine rule is easier to use, but since sin(A) = sin (180-A), sometimes the sine rule will yield an ambiguous answer.