1 将线段AB延长至C,使BC=1/3AB（BC=三分之一AB）,延长BC至D,使CD=1/3BC,延长CD至E,是DE

1 将线段AB延长至C,使BC=1/3AB（BC=三分之一AB）,延长BC至D,使CD=1/3BC,延长CD至E,是DE=1/3CD,若AE=80cm,求AB的长
2 已知线段AB=5cm,延长AB至C,使AB=7cm,在AB的反方向延长线上取D,使BD=4BC,设CD中点为E,求线段AE是CD的几分之一?
(希望有算式)

1.设AB长度=a
BC=1/3a
CD=1/3*1/3a
DE=1/3*1/3*1/3a
AE=a+1/3a+1/3*1/3a+1/3*1/3*1/3a=80 =>a=54
2.AB=5,AC=7 =>BC=2
BC=2 BD=4BC =>BD=8
BC-AB=AD =>AD=3
=>CD=10
=>DE(CE)=5
DE-AD=AE =>5-3=2
AE=2,CD=10 =>AE=1/5CD