I'm a letter.
I am found in an elephant and oh! I am heard too, by a person sense of hearing!
Sometimes, I am also used in a cartesian plane, or maybe used as a word to describe things are growing really.. really fast.. unless I am negative :/.
I am a letter, but found commonly in letters! And I am also sometimes commonly known as a latter (In English).
Beat that! I'm inbetween the lines of music that have a very troubled chef.... just below the highest "seen" staff. Look at that buns I just made! (I know it's bad)
I'm used in banks after I was discovered by approaching to a limit. I mean, I was discovered to have numeric use.
A child uses me when in digust (sometimes).
Oh... I'm so rational... NOT.
So... what am I? (I also like to see how you explain the paragraphs that I written. The difficulty is just why that letter represents some of the paragraphs. Not the guessing :/.)
Clue 1 (Beat that!....just made!):
Change a "b" to a "p" in that paragraph and you notice the paragraph is.. literally... sigh.
Clue 2 (And...English)
Vowels. But even if you explain all the paragraph correct except for this, I would accept your full explanation answer because that sentence is ambiguous. Sorry. "vowels" is what I have in my mind.
Clue 3 (I'm used in banks... numeric use):
How do you think I was mathematically discovered. I mean, English already created me but it took a while before mathematics discovered me.