How do you compute the dot product to find the magnitude of #u=12i-16j#?

1 Answer
Jul 6, 2016

Answer:

#abs vec u = 20#

Explanation:

you should dot it against itself

by definition #vec u * vec v = abs vec u abs vec v cos psi#

if #vec v = vec u# then #psi = 0# and so #vec u * vec u = abs vec u abs vec u cos 0 = (abs vec u)^ \color{red}{2}#

so #<12, -16> * <12, -16 > = (12)(12) + (-16)(-16) = 400= (abs vec u)^ \color{red}{2}#

so #abs vec u = sqrt 400 = 20#