



 
Hi Nazrul, The easiest way to prove these equivalent statements about vectors is geometrically, I'll just show the first one: Remember that vector a means that it has the same magnitude (length) as vector a but an opposite direction. If you draw any vectors a & b their resultant vector is a+b. If you draw vectors a &b their resultant vector is a+(b)=ab. If you draw (a+b), it coincides with ab. Hope this helps, Janice
 


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