G is the center of gravity, then AM is the center line.
∴AG/AM=2/3,CM= 1/2BC
∫GD∨BC
∴△ADG∽△ACM
∴DG/CM=AG/AM=2/3
∴DG/( 1/2BC)=2/3
That is DG/BC= 1/3.
2、∫GE∨AC、GF∨AB
Similarly: GE/AC= 1/3, GF/AB= 1/3.
∴gd= 1/3bc,ge= 1/3ac,gf= 1/3ab
∴GE+GF+GD
= 1/3(AC+AB+BC)
= 1/3× 12
=4