Consider the vectors

vec$(a)=3$vec$(i)$ vec$(j)-$vec$(k),$vec$(b)=$vec$(i)$ vec$(j)4$vec$(k),$vec$(c)=-3$vec$(i)-$vec$(j)$ vec$(k)$

vec$(d)=3$vec$(i)-$vec$(j)$ vec$(k),$vec$(g)=-$vec$(i)-3$vec$(j)$ vec$(k)$

Which pairs $($if any$)$ of these vectors are

$($a$)$ Are per Your first pair is incorrect

$(a,c),(b,g)$

$($Enter none or a pair or list of pairs, e$.$g$,$ if vec$(a)$ is perpendicular to vec$(b)$ and vec$(c),$ enter $(a,b),(a,c).)$

$($b$)$ Are parallel?

$($Enter none or a pair or list of pairs, e$.$g$,$ if vec$(a)$ is parallel to vec$(b)$ and vec$(c),$ enter $(a,b),(a,c).)$

$($c$)$ Have an angles less than $\frac{}{2}$ between them?

$($Enter none or a pair or list of pairs, e$.$g$,$ if vec$(a)$ is at an angle less than pi$/2$ from vec$(b)$ and vec$(c),$ enter $(a,b),(a,c).)$

$($d$)$ Have an angle of more than $\frac{}{2}$ between them?

$(a,c),(b,c),(b,d),(b,g),(c,d),(c,g),(d,g)$

$($Enter none or a pair or list of pairs, egg, if vec$(a)$ is at an angle greater than pi$/2$ from vec$(b)$ and vec$(c),$ enter $(a,b),(a,c).)$