This is a free lesson from our course in Trigonometry
This lesson defines and deals with the basic concepts of laws of sines and cosines and their applications. The Sine Law :
When you need to work with triangles that have no right angles, you can use the
Sine Law. This law can be used when you know 3 pieces of information about the triangle
and one known side is directly across from a known angle. If we dont have this
last property, we need to use the Cosine Law. The Cosine Law :
As explained above, sometimes we have situations where the sine law will not work.
This happens when we do not have a side which corresponds to an angle in the triangle.
In such cases, we use the Cosine Law. (More text below
video...)
(Continued from above) For a triangle ABC with sides a, b, and c
and opposite angles A, B and C, the law of sines is:
sin A
/ a = sin B / b = sin C / c
For the same sides and angles, laws of cosines are:
c2
= a2 + b2 - 2ab cos C.
b2
= a2 + c2 - 2ac cos B.
a2
= b2 + c2 - 2bc cos A.
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