Can someone show me the math for this..

[pudley4]

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What I want to know is that since he is making a positive expectation play by calling your bet, you must be making a negative expectation play by betting into him

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No, this is wrong.

You are correct in betting because you are the favorite to win the hand. Therefore you're making money on every single bet that goes in.

He is therefore losing money on every bet that goes in; however, the money that's already in the pot more than makes up for what he's losing by calling your bet. (And this explanation is another way to describe pot odds.)