Trigonometry: Definition - Law of Sines & Cosines
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 don’t 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...)
<h2> Trigonometry - Law of Sines & Cosines</h2> <p> triangle, laws of sines and cosines, right triangles, basics, example, solution, trigonometric functions, sine, cosine, laws of sine, laws of cosine, side length, sides, angles, math help, practice questions, quizzes</p> <p> 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 csquare = asquare + bsquare – 2ab cos C, bsquare = asquare + csquare – 2ac cos B, asquare = bsquare + csquare – 2bc cos A.</p>
Other useful lessons:
Using the law of Sines and Cosine Formulas
The Ambiguous Case
Area of a Triangle
(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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