- #1
iScience
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say i have some vector ##\vec{v}## multiplied by a scalar k.
the norm of ##\vec{v}## would be just ##||\vec{v}||## and the norm of ##k\vec{v}## is claimed to be ##|k|||\vec{v}||## ie, ##||k\vec{v}||=|k|||\vec{v}||## ie the sign of the constant is irrelevant.
when i work it out..
$$||k\vec{v}||=\sqrt{(kv_{1})^2+(kv_{2})^2+(kv_{3})^2+...}$$
$$=\sqrt{k^2(v_{1})^2+k^2(v_{2})^2+k^2(v_{3})^2+...}=\sqrt{(k)^2[(v_{1})^2+(v_{2})^2+(v_{3})^2+...]}$$
from this point, yes i could say that since all k values are squared, the square root must be a positive value. but take k to be a negative number (-a) and say we don't actually compute the square of k and we just leave it in ##(-a)^2## form. we can do the following
(continued from previous)
=$$\sqrt{(-a)^2}\sqrt{(v_{1})^2+(v_{2})^2+(v_{3})^2+...}$$
in which case, the ##\sqrt{}## and the ##(-a)^2## can cancel out which would then return our original -k value which is negative. (where -k=-a)
i'm pretty sure there's an error some where in my line of reasoning though, could someone please find it?
the norm of ##\vec{v}## would be just ##||\vec{v}||## and the norm of ##k\vec{v}## is claimed to be ##|k|||\vec{v}||## ie, ##||k\vec{v}||=|k|||\vec{v}||## ie the sign of the constant is irrelevant.
when i work it out..
$$||k\vec{v}||=\sqrt{(kv_{1})^2+(kv_{2})^2+(kv_{3})^2+...}$$
$$=\sqrt{k^2(v_{1})^2+k^2(v_{2})^2+k^2(v_{3})^2+...}=\sqrt{(k)^2[(v_{1})^2+(v_{2})^2+(v_{3})^2+...]}$$
from this point, yes i could say that since all k values are squared, the square root must be a positive value. but take k to be a negative number (-a) and say we don't actually compute the square of k and we just leave it in ##(-a)^2## form. we can do the following
(continued from previous)
=$$\sqrt{(-a)^2}\sqrt{(v_{1})^2+(v_{2})^2+(v_{3})^2+...}$$
in which case, the ##\sqrt{}## and the ##(-a)^2## can cancel out which would then return our original -k value which is negative. (where -k=-a)
i'm pretty sure there's an error some where in my line of reasoning though, could someone please find it?
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