if a = (1,-1 ) & b = (-2,m)  r 2 collinear vectors den m=? ive got it as 2 but d ans is 2 & 4 how is it  4 giv d procedure

if vectors a i +2bj  +a k &  (2b-c) i+(3a+c)j +bk  r parallel den unit vector in der direction is ans is

1/ (2i +3j+2k) but got it as 1/ ( i+ 3j +k)  how is it ?  plz tell d method