Respuesta :

mathmate
a · b = |a| |b| cos(theta)
=|a| * 14 * cos(45)

a · b |a| =3 
=>
|a| * 14 * cos(45) * |a| =3
|a| ² =3/(14cos(45))
|a| = sqrt(3/(14cos(45)))
=0.63868 (approx.)