chiro,

I did not quite get you, are you saying I should get rid of denominators and substitute x as x'-a (or x'+a?)? How can I put x'=x+a?

I am sorry, I'm not acquainted with the properties of norms as you are saying.

Gusbob,

I tried your approach but no success yet,

at most I got,

Attachment 28550
OR by using (a+b+c)^2 identity:

Attachment 28551
But I'm stuck at that. Thanks for your replies anyway, please do reply if you have any idea what to do next.

PS. I have no idea why the latex is appearing so small.