How to Derive the Law of Cosines Formula

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In this video, we will learn how to derive the Law of Cosines formula. We will draw an oblique triangle ABC and place it on the coordinate plane where the vertex B is at the origin. This will give us points (a, 0) and (c cos B, c sin B). We can then use the distance formula to find the distance between those two points. We will then simplify and manipulate our result to match the Law of Cosines Formula.

Chapters:

00:00 Introduction
00:16 Understanding the notation
01:57 Labeling our image part 1
02:36 A common mistake with labeling (x, y)
03:43 Changing (x, y) to (c cos B, c sin B)
04:49 Plug into the distance formula
05:41 Square both sides
06:10 Simplify
07:30 Matching the Law of Cosines

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