I have a question about Penetration monster 0 %resistant

if i have 1000 dmg and 40% penetration attack a monster with 0 % resistant dmg will 1400 or 1000 ?
thanks you :D

I thought negative res could go down to come value in the -70s, but I'm sure someone will be along with the most mathematically sound response soon enough. But what you asked should be correct until you hit that negative cap.

Penetration monster?

huh?...

http://pathofexile.gamepedia.com/Resistance_penetration

If the monster has 0% resistance, 40% penetration will increase damage by 40% (this is a more multiplier). However, this changes if the monster has a resistance value other than 0%. If you have a look at the plot on the wiki page, you will see that the multiplier increases if the monster has positive resistance and the other way around for negative resistances (the y axis of the plot is wrong, btw. and should be multiplied by 10).

There is no 'negative cap' for resistance penetration. Technically you can have -10000% resistance ( https://www.pathofexile.com/forum/view-thread/59271/page/2#p751660 ).

thanks :D