# Prompt 3: The Cosine Rule 1

1. Which formula do you use for the cosine rule? A formula that isn’t listed above?

2. Why might you stress the importance of number 2?

3. Is there a context in which you would consider teaching number 3? Is it a problem that this doesn’t appear in textbooks or formula books?

## 2 thoughts on “Prompt 3: The Cosine Rule 1”

1. I think you’re missing a ^2 on the left-hand side of that third equation.

In the first one, I would permute the variables so that c is on the LHS. This avoids the double c in b c cos (which when typing could also be avoided by using \cos instead of cos but I’d still avoid this because the distinction is harder to make in handwriting).

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2. curmudgeon says:

I prefer going visual with the connection to the geometry rule SAS.

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