Is -RES multiplicative?

[Latex]

I've always wondered if -RES is multiplicative, because I seem to get more value out of it over +DMG

For example say my Damage is at 400% from a /Kin boost, the target has -50% RES applied, would I do 600% Damage? Or would I do 450%?

[Luminara]

Yes.  Damage total * 1.(-Res).