Question

what is preposition? explain, x-y>5 is a preposition or not?

Answer 1

i guess you are asking about proposition,

Any statement which is uniformly either true or false can be called proposition.
ex- capital of India is new Delhi, this statement is universally true so it is proposition,
     -( 2+3=6 ) this statement is false so it is also proposition..
x-y>5 can not be stated as proposition because we can not say if its true or false unless value of x and y is defined.

if you satisfied with answer then rate it,
however if your question was about preposition then,

A preposition is a word or a set of word that indicates location or some other relationship between a noun or pronoun and other parts of the sentence.
ex (about, after, besides, instead of, in accordance with).
ex- book is on the table,