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                                    If vec(a),vec(b),vec(c )are three non coplanar vector such that vec(a)+vec(b)+vec(c )=alphavec(d) and vec(b)+vec(c )+vec(d)=betavec(a), then vec(a)+vec(b)+vec(c )+vec(d) is equal to | 
                            
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Answer»  `vec(0)` `impliesvec(a)+vec(b)+vec(c)=alpha(betavec(a)-vec(b)-vec(c))IMPLIES(1-alphabeta)vec(a)+(1+alpha)vec(b)+(1+alpha)vec(c)=vec(0)` `impliesalphabeta=1,alpha=-1{because vec(a),vec(b),vec(c)" arenon COPLANAR"}implies alpha=beta=-1` `becausevec(a)+vec(b)+vec(c)=alphavec(d)impliesvec(a)+vec(b)+vec(c)+vec(d)=vec(0)`  | 
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