If \(\vec a \:and\: \vec b\) are two vectors such that \(|\vec a + \vec b|= |\vec a - \vec b|=4,\) then which one of the following is correct?
1
\(\vec a \:and\: \vec b\) must be unit vectors.
2
\(\vec a\) must be parallel to \(\vec b.\)
3
\(\vec a\) must be perpendicular to \(\vec b.\)
4
\(\vec a\) must be equal to \(\vec b.\)