It is found that \(|\vec{A}+\vec{B}|=|\vec{A}|\). This necessarily implies:

1. \(\vec{B}=0\)
2. \(\vec{A},\) \(\vec{B}\) are antiparallel
3. \(\vec{A}\) and \(\vec{B}\) are perpendicular
4. \(\vec{A}.\vec{B}\leq0\)