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 Hi Teachers

Please help me to figure out what these phrases mean

1.I can agree with you more
2.I can't agree with you more
3.I can disagree with you more
4.I can't disagree with you more
5.I couldn't agree with you more
6.I couldn't disagree with you more
7.I could agree with you more
8.I could disagree with you more 
 What do the above phrases mean? Thanks 
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I agree that these are the only two options that are used in reality:

5.I couldn't agree with you more

6.I couldn't disagree with you more

The other options are just playing around with the language, but if no-one ever says those things, then why bother? They just sound very odd and are effectively meaningless.
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Sentences 5 and 6 are commonly used expressions.

5. I couldn't agree with you more. => This means I agree with you completely. I agree 100%, and it's not possible to agree more than that.

6. I couldn't disagree with you more. => This means I disagree with you completely. I disagree 100%, and it's not possible to disagree more than that.

Sentence 2 might be used to mean the same thing as 5.

Sentences 1, 3, 4, 7, and 8 are not used as "standard" expressions, and without any further context, they only sound odd to me.
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Comments  
YankeeI couldn't disagree with you more.
A double negative often equals the related positive. For example, I did not miss that dance (means I went to it). I could not disagree with you more, on the other hand and even though it seems to have two negatives (not and disagree), does not mean "I agree". So what are the component parts of the statement?

Subject=I, Verb=disagree, Prepositional phrase modifying the verb = with you. As for the other words, I speculate that "could not ... more" effectively constitutes an "adverb phrase", which serves to intensify the verb. What do you think?
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I am also wondering that, couldn't disagree with u more, this sentence has double negative, would that a positive statements that means 100% agree with someone