1.∵DC=AD=1/2ACCE=BE=1/2BC
AB=AC+BC=5
DE=DC+CE
∴DE=DC+CE=1/2AC+1/2BC=1/2(AC+BC)=1/2AB=2.5
∵2.5=1/2×5
∴DE=1/2AB
2.∵DC=AD=1/2ACCE=BE=1/2BC
AB=AC+BC=a
DE=DC+CE
∴DE=DC+CE=1/2AC+1/2BC=1/2(AC+BC)=1/2AB
∴DE=1/2AB
1.∵DC=AD=1/2ACCE=BE=1/2BC
AB=AC+BC=5
DE=DC+CE
∴DE=DC+CE=1/2AC+1/2BC=1/2(AC+BC)=1/2AB=2.5
∵2.5=1/2×5
∴DE=1/2AB
2.∵DC=AD=1/2ACCE=BE=1/2BC
AB=AC+BC=a
DE=DC+CE
∴DE=DC+CE=1/2AC+1/2BC=1/2(AC+BC)=1/2AB
∴DE=1/2AB