Math Wizard's How much % Damage Reduction to reach Cap While Cursed with Amplify Damage?

OK so need some calculations done and in the right order please. Did a search but didn't yield any result and I've been thinking about this for years as crazy as that sounds.

If I get cursed as a player by an enemy which seems to happen about every 30 second on Hell difficulty,

could some kind soul walk me through the math and steps to figure This out.

% Damage Reduction is capped at 50% right?

So how much % Damage Reduction would be needed to still reach that cap while cursed with Amplify Damage on self?

150%??!!

Good ol' Arreat Summit says "Amplify Damage lowers monster Physical Resistances by 100%"

So would it be -100% + 150% = 50% Damage Reduction (the Cap)??

Math gets my head spinning when I just wanna have fun, so please need a wizard to help with

this conundrum. Blessing of Arkaine upon Thee!