In this post, we discuss the proof behind one of the most commonly used identities in trigonometry. We examine the equations below and show why the relationships always hold. To students who have taken trigonometry, I’m sure that you have met these equation before. The proof of these equations are as follows. Consider triangle right […]

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# High School Trigonometry

## An elementary proof of the cosine law

The cosine law states that in triangle with side lengths and , the following equations are satisfied: * The discussion below shows how these equations were derived.

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