Hi guys.
I need to prove Bessel's inequality for a finite set of orthonormal vectors
I looked around the internet and found this on Wikipedia:
"Bessel's inequality follows from the identity:
"
but something just does not make sense to me.
how did they make the first transition from to ?
you can't just use the binomial expanding formula here, can you?
Is there another, more simple proof for this inequality?
Thanks in advanced!