AO=1/2*AC=1/2*(AB+AD)=1/2*a+1/2*b ;
BO=AO-AB=1/2*a+1/2*b-a= -1/2*a+1/2*b ;
AE=AB+BE=AB+1/3*BC=AB+1/3*AD=a+1/3*b ;
BE=1/3*BC=1/3*b .
AO=1/2*AC=1/2*(AB+AD)=1/2*a+1/2*b ;
BO=AO-AB=1/2*a+1/2*b-a= -1/2*a+1/2*b ;
AE=AB+BE=AB+1/3*BC=AB+1/3*AD=a+1/3*b ;
BE=1/3*BC=1/3*b .