Let $Q(\vec{x}) = \vec{x}^TA\vec{x} $
Im trying to go from Q(2x) = 4Q(x).
What I have is $Q(2\vec{x})=(2\vec{x})^TA(2\vec{x})=4 \vec{x}^TA\vec{x}=4Q(\vec{x})$,
but I'm worried I'm using some undefined properties of multiplication. I just moved the 2's to the front, but again, am not sure if that's allowed.
Any input would be great, thanks.