Clear[x,y,z,a,v,u,d];

a={{2,3,1},{1,3,0},{1,2,1.5}}
MatrixForm[a]

v=a[[2]]-a[[1]]

u=a[[3]]-a[[2]]

Plot1=Graphics3D[{Opacity[0.5],Sphere[a[[1]],0.1],Sphere[a[[2]],0.1],Sphere[a[[3]],0.1],Sphere[v,0.05]}];
Plot2=Table[Graphics3D[Text[i,a[[i]],{1,0}]],{i,1,3}];
Plot3=Graphics3D[{Arrowheads[.05],Arrow[{a[[1]],a[[2]]},0.02],Arrow[{a[[2]],a[[3]]},0.02],Arrow[{a[[3]],a[[1]]},0.02]}];
Show[Plot1,Plot2,Plot3,{Axes->Automatic,AxesLabel->{x,y,z},AspectRatio->Automatic,PlotRange->Automatic, SphericalRegion->True}]

d=Norm[a[[2]]-a[[1]]]

a[[1]].a[[2]]

w=u×v
w=u.v

Plot4=Graphics3D[{Arrowheads[.05],Arrow[{w},0.02](*,Arrow[{w[[2]],w[[3]]},0.02],Arrow[{w[[3]],w[[1]]},0.02*)}];

Show[Plot1,Plot2,Plot3,Plot4,{Axes->Automatic,AxesLabel->{x,y,z},AspectRatio->Automatic,PlotRange->Automatic, SphericalRegion->True}]