in need of help!

bestie

New member
Joined
Apr 26, 2014
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1
Points A, B, C and D are defined by position vector a, b, c and d respectively.
If AB +CD = 0
Prove that ABCD is a rhombus if IaI = IcI and angles AOB and BOC are equal

what i have done so far.
AB = AO+OB = -a +b
BC = BO +OC =-b+a

Thank you
 
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