# Proof (vectors, norm, and dot product)

• November 12th 2009, 06:28 AM
elitethut
Proof (vectors, norm, and dot product)
Never-mind, I found the problem.
• November 12th 2009, 08:55 AM
tonio
Quote:

Originally Posted by elitethut
Hi everyone !

I want to solve the following:

$1/4||\vec{u}+\vec{v}||^2-1/4||\vec{u}-\vec{v}||^2=\vec{u} \cdot \vec{v}$

I have no idea how to start this proof...anyone can help ??

Thanks !

Definition: $||\vec{u}||^2:=\vec{u}\cdot \vec{u}$, so now you have an idea how to begin here.

Tonio
• November 12th 2009, 08:58 AM
redsoxfan325
Quote:

Originally Posted by elitethut
Hi everyone !

I want to solve the following:

$1/4||\vec{u}+\vec{v}||^2-1/4||\vec{u}-\vec{v}||^2=\vec{u} \cdot \vec{v}$

I have no idea how to start this proof...anyone can help ??

Thanks !

Nevermind. I think I goofed.