Study GuideTrigonometry–Trigonometry of Triangles1. Law of CosinesFigure 1 Reference triangle for Law of Cosines.In the previous section, you learned how to solveright triangles. Now, we’re going a step further. Inthis section (and the next one), you’ll learn formulas that work forany triangle—whether it’sright,acute, orobtuse.Let’s start by setting up the triangle.•Letα, β,andγbe the three angles of a triangle.•Leta, b, and cbe the lengths of the sides oppositeα, β,andγ,respectively.With this setup, we can write three very important formulas.1.1The Law of Cosines FormulasTheLaw of Cosinesconsists of these three equations:Each equation relatesone side of the triangleto theother two sidesand theangle between them.Together, these formulas allow us to solve triangles that arenotright triangles.Preview Mode
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