- #1

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## Homework Statement

How do you show |r_1-r_2| is rotationally invariant

## Homework Equations

## The Attempt at a Solution

So i get that we need to show that it is invariant under the transformations

## r_1 \rightarrow r_1 + \epsilon (n \times r_1)##

## r_2 \rightarrow r_2 + \epsilon (n \times r_2)##

but that gives

## |r_1 + \epsilon (n \times r_1) -r_2 - \epsilon (n \times r_2)|##

and i can't see what this equals ##|r_1 -r_2|##

Many thanks