# Is <-x,-x> = <x,x> ?

1. Sep 2, 2008

### coverband

Is <-x,-x> = <x,x> !!!!!!?

Thanks!

2. Sep 2, 2008

### HallsofIvy

Re: Is <-x,-x> = <x,x> !!!!!!?

That depends on what you mean by <x, x>!

Some people use it to mean a 2 vector. In that case, <-x, -x>= <x, x> only if x= 0. Other wise, <-x, -x>= -<x, x>.

But you may be referring to an inner product in some vector space. If that is so, then <-x, -x>= -< x, -x> = -(-<x, x>)= <x, x> so that is, in fact, true.