- #1

David92

- 3

- 0

## Homework Statement

So I can't get from line (53) to line (54)

I do not understand how interchanging the variables will cause the imaginary part to disappear

## The Attempt at a Solution

I'm not sure where to start

I know exp(ix) = cos(x) +isin(x)

And the only way i see cos(x) coming out is using the exponential identity

exp(ix) + exp(-ix) = 2cos(x) (but this clearly isn't it)

But this 'interchanging' variables really doesn't make sense to me

Please help! The answer is apparently obvious! haha