The Law of Sines and the Law of Cosines
So far in this unit, we have learned how to find angle measures and side lengths of right triangles using the six trigonometric ratios. Although these are helpful, alone they are restricted to use with right triangles only. In this section, we are going to learn two equations (formulas) that allow us to apply the functions to triangles that are not right triangles (although these formulas would work with right triangles as well).
The two formulas that we are going to learn are the Law of Sines and the Law of Cosines. Each one is used when specific information is known about a triangle.
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The Law of Sines is used when we know:
The Law of Cosines is used when we know:
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When working through the problems, first write down the information given and then decide which formula you will use based on what information you have.
