Hi everybody!

I guess the title is clear, but to clarify it more, I want to know the difference between these words. I know a bit about the differences, but I need a precise answer. especially about these three: "Hi, Hi there, and Hello"
so, I really appreciate it in advanced, anyone who can give me a complete answer or if you can ask your teachers and answer me.

Thank you my friends

I just couldn't help it and wanna say my point of view of these words that you mentioned
nowdays "hi" has become kind of formal greeting and in the movies which I have watched so far, when you wanna greet someone who is a stranger you say " hi" ............ And for someone whom you recongnize you use "hi there" especially when the person you're greeting is not aware of you
"and in recent months I witness that in the movies, people even greet one another by saying "hey
!!!!

I really appreciate your concern, Mohammad.
yeah, that's the case. I usually hear it a lot, even in formal situations, I mean in movies, and that's why I am a little bit confused. Because we were told that HI is used in INFORMAL situations.
about "Hi there" I remember a teacher of mine, always used "hi there" as the greeting of class.
and again, about hey, yes. I agree. I exactly came across this one in movies, greeting by "hey" or "hey there" . but I guess it's too informal, isn't it?

yes, " hey" is the most infomal type of greeting
anyway
people change and so does their language

according to what I've seen and learnt till now
hello is a formal way of greeting and hi is informal.
in fact hi is use in friendly talking and speaking
and about "hi there" as you said and I've heard about , it is used in facing to a group. for example the teachers use this word for starting up their classes.
and again you're right that every decade beside changing the people's habits and cultures, their literature and language points are getting changed

.thank you Sedna, good points dear

you're welcome honey