Can F_1,2 Be Defined Using r-hat_2,1 Instead of r-hat_1,2?

[Ryan McParlan]

In this example (https://imgur.com/a/pTFIt) could i define F_1,2 in terms of r-hat_2,1 instead of r-hat_1,2?

 

[Doc Al]

In this example (https://imgur.com/a/pTFIt) could i define F_1,2 in terms of r-hat_2,1 instead of r-hat_1,2?

Sure, why not? As long as you take into account that they have opposite directions.