# Euclid II 12 The Law Of Cosines Obtuse

- Author:
- Gary Rubinstein

- Topic:
- Cosine

## Proving The Law Of Cosines

To prove The Law Of Cosines (circa 250 BC method), explain why the blue square must have the same area as the sum of the yellow square, the gray square, and the two orange rectangles.

## Comparing the ancient and the modern ways of thinking about The Law Of Cosines

Explain how this ancient way of explaining The Law Of Cosines, without any mention of the word 'cosine', is equivalent to our modern formula of