i did'nt asked any homework question
instead i asked the validity of a given formula
see this question
Adapted from my comments.
From one of the links in the homework close reason:
A "homework question" is any question whose value lies in helping you understand the method by which the question can be solved, rather than getting the answer itself.
Surely your question asks exactly that: how do I solve/prove this? So we've established that it falls under the homework-category, right? Now how do you get the question reopened? By showing what you have done to try and get the answer: links to websites you've visited (with some explanation of what's on there) and of course your own work.