That is not a usage I am familiar with!
If I saw it as an editor, I would write notes to the author of, "What do you mean here?"
Was the drama's author a native English speaker?
Was the drama a translation into English from some other language?
Was there some other context going on such that person B was not responding to A's most recent comment?
Or, to answer your question...
No, in American English, at least, "I'm positive" doesn't mean "I agree with you," nor can "
I'm negative" mean
"I disagree with you.
" I could contrive situations where similar constructions could be understood as agreement/disagreement, but I would have to set up idiosyncratic speech patterns for Person B, where B tended to shorthand "
I'm positive you are right" to just "I'm positive."
ell.stackexchange.com/users/15827/A.Beth
I am positive means
I'm certain .
It's usually used when there is reason to express certainty in some statement.
So, you could say: — Do you think it will be cold tomorrow?
— I'm positive!
but not — It's cold today.
— I'm positive.
Here are some other questions that might be followed by
I'm positive :
Are you sure it's safe?
Are you capable of delivering the product on time?
Are [sports team name] going to win tonight?
Do you think the weather will be good enough for a picnic on Saturday?
Did John understand the requirements?
Notice that not all of them ask whether the person is sure, but they do all require the respondent to make some kind of judgement, which is why it is possible to respond with "
I'm positive"; it's expressing the degree of certainty in that judgement.
Did you buy bananas?
This is slightly different.
Normally, the answer to this, if you bought bananas, would simply be "Yes".
However, there is a context in which you might say "I'm positive" - basically if there's some reason to not be certain of the result.
For example, person A goes to the fruit bowl (where there are no bananas, despite asking person B to buy some) and says, "Did you buy bananas?"
Then person B looks in the fruit bowl, looks in the shopping bag, glances all around the room and says, "I'm positive I bought them!"
before finally finding them in the cupboard.
N.B.
There is also another meaning of I'm positive that would be apparent in a different context - namely if you have been tested for something.
For example, I was tested for HIV
and I'm positive.
That means that the speaker is HIV-positive .
ell.stackexchange.com/users/3976/starsplusplus
The answer to the question is 'No'.
The use of 'I am positive' in relation to the statement 'It is cold today' results in a non-sequitur; the response refers to the speaker, and not the weather.
Strictly speaking, the phrase "I'm positive" should allude to something about which the person is positive, since it is an assertion of belief.
("Are you sure you left your keys on the table?"
"Yes, I'm positive!").
Sometimes it is used similarly to 'upbeat' or 'optimistic', to refer to the person:
"I've been unemployed for two years", said Bill, the electrician, "but I'm fairly positive!"
ell.stackexchange.com/users/14067/Simon Drew
I have come across this usage of 'positive' too many times in English movies and tv serials.
This usage translates extremely well into my regional language.
But since I have to explain it in English I'll try to be as accurate as possible.
This 'positive ' is used when you are extremely sure about something.
Suppose someone asks you Are you sure you
it was Tim who you saw in the mall last night ?
Now how would you respond to express that you're extremely sure.
You'd say, Positive.
Are you good enough to drive right now ?
Positive.
(Though I have had few drinks, I am confident that I'll still be able to drive)
Let's modify your example A - It's too cold out here, isn't it ?
There are two ways to answer it 1.
Yeah, certainly it is !!
or when you think that it's way too cold out here, then you might respond with just one word i.e. 2.
Positive.
However I have never come across the usage where you say 'I am positive' in the above examples. '
I am positive' doesn't sound good english.
You don't have to say 'I am positive'.
Responding only with 'positive' will do the job.
Note - this is a bit informal usage.
It has a meaning similar to 'very sure.'
ell.stackexchange.com/users/11113/Leo
Q: "I'm positive" can have meaning
"I agree with you"?
A:
No.
Well, could be (sort of).
Q: and is "I'm negative" that "I disagree with you"?
A:
No.
Well, could be (sort of).
It looks like it's Asian English.
I think this is the best way to translate them (even though dictionaries would define positive as "completely certain ):
I'm positive
= I think 'yes'.
I'm negative =
I think 'no'.
So, replying "Oh, Today is very cold" with "I'm positive" doesn't really mean "I agree with you", but it's more like
"I'm positive (that today is very cold)", or in other words, "I think yes, today is very cold", and that's why I said "I'm positive" could be understood as "I agree with you".
(Because I'm certain about the same thing you're thinking of.)
So, no, it doesn't literally mean "I agree with you", but yes, it could convey roughly the same idea.
The same applies to "I'm negative".
I hope this helps.
ell.stackexchange.com/users/3281/Damkerng T.
In a drama, I heard the following exchange:   person A : Oh, Today is very cold.  person B : I'm positive.   So I thought that  "I'm positive"  means  "I agree with you" , but after googling it seems like that there is no such meaning.  Can  "I'm positive"  have the meaning  "I agree with you" ? What about  "I'm negative"  - can that mean  "I disagree with you" ?
Does "I'm positive" mean "I agree with you"?
ell.stackexchange.com
<adjectives>
ell.stackexchange.com/questions/49176
ell.stackexchange.com/users/3525/Jason Heo
Strictly speaking, the phrase "I'm positive" should allude to something about which the person is positive, since it is an assertion of belief. However, this could be understood as "I agree with you" in the sense of  "I'm positive (that today is very cold)", or in other words, "I think yes, today is very cold, and that's why I said "I'm positive". Positive refers to belief/certainty in this instance.
Positive refers to belief/certainty in this instance.