Talk:Last Whisper/@comment-8053512-20140209172751/@comment-20804982-20140218232754

So before you land the E, you are doing

100/(100 + Armor)

After you are doing

100/(100+ ((1 - %pen) * Armor)

So to calculate the increase from pre-E to after-E, it is just the second formula over the first formula, which simplifies to

(100 + Armor) / (100 + ((1-%pen) * Armor))

So for urgot's E at 20%, the formula for the increase in damage is:

(100 + Armor) / (100 + (.8 * Armor) = % increase in damage