AC:CD:CB=1:2:4说明D是CB中点,即CD=DB,CD=2AC
所以MN=1/2*AC+CD+1/4*DB,
设比例系数为X,则AC=X,CD=2X,DB=2X;
AC+CD+DB=X+2X+2X=5X=AB即X=14/5,
MN=1/2*X+2*X+1/4*2*X=42/5
AC:CD:CB=1:2:4说明D是CB中点,即CD=DB,CD=2AC
所以MN=1/2*AC+CD+1/4*DB,
设比例系数为X,则AC=X,CD=2X,DB=2X;
AC+CD+DB=X+2X+2X=5X=AB即X=14/5,
MN=1/2*X+2*X+1/4*2*X=42/5