Rift
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I think I understand the question now. By "вычитается" (deducted), I meant the same as you mean by "снимается" (removed) – then everything is correct, let's calculate together: golem (75% resistance – magic protection) minus the effect of irresistible force (75%). The effect is not 75 - 75, but 75% of the hit score (HS) is deducted as a percentage from the golem's protection. And then it's simple math: :)
1). 75% of 75 = 56.25% - this is how much HS the irresistible force penetrates the protection;
2). 75% - 56.25% = 18.75% - this is how much the golem will reduce the damage received;
3). 990/100 x 18.75% = 185.625 - approximately this is the amount of damage the golem should not receive in your case, if we don't take into account the error. It seems to fit the "almost 200 damage absorbed". :)