→           →
In this question, candidates were expected to compute vectors  XY  and YZ                      
from the given co-ordinates of the points.     
                 →                                               
                XY  =    ( 6 - 4)     =    2    , YZ   =     ( -2-6)      =   ( -8)
                             ( 2 - 0)           2                      ( 1 -2)            (-1 )                                             
                                                           →       →
With these, they can simplify    2XY + 3XZ.  However, a good number  of the candidates
                  →
had it that XY  =  √(6-4)2 + (2-0)2 i.e distance between X and Y which is very wrong.     
              →                                                                                                              
In 7(b), XZ   =   -6  ,  thus /XZ/ = √(36+1) = √]37.   Hence required unit vector is         
                            1                                                                                                                  
   1     (-6)       or     1  (-6i + j)
√37   (-1)              √37       

Rationalizing the denominator gives √37  (-6) .  Many candidates did not rationalize
                                                                    37   (1)
 the denominator hence, lost the final mark.