Hello again, another vector question. The diagram (not included) shows a parallelogram OABC with OA=a and OC=c; AC and OB intersect at point D such that OD=hOB and AD=kAC. How do I show what h and k equal? I managed to achieve: a+c=2DB+AD-DC=2OD+DC-AD=OB and c-a=2DC+OD-DB=2AD+DB-OD=AC Furthermore, I know that AD+DB=OD+DC and OD-AD=DB-DC I can 'see' that h and k = 1/2; but how do I show it? As always, the help is appreciated. I love you people :).