AB = 20cm, C and D are two points on the line AB, CD = 8cm (1). If e is the midpoint of AD and F is the midpoint of BC, find the length of EF. (Fig. 1) (Fig. 1) a --- C --- e -------- D --- f -------- B (2) If you translate CD along the ray AB to the extension line of AB, what is the length of ef?

AB = 20cm, C and D are two points on the line AB, CD = 8cm (1). If e is the midpoint of AD and F is the midpoint of BC, find the length of EF. (Fig. 1) (Fig. 1) a --- C --- e -------- D --- f -------- B (2) If you translate CD along the ray AB to the extension line of AB, what is the length of ef?

1、AE=DE=1/2AD
BF=CF=1/2BC
AD+BD=AC+CD+CB=AB+CD=20+8=28
∴AE+BF=1/2(AD+BC)=1/2×28=14
Ψ EF = ab - (AE + BF) = 20-14 = 6cm
2、AE=DE=1/2AD
BF=CF=1/2BC
AD=AB+BC+CD
AD+BC=AB+BC+BC+CD=28+2BC
∵AE+CF=1/2(AD+BC)=14+BC
∴EF=AD-CD-(AE+CF)=AB+BC+CD-CD-(14+BC)
=AB-14
=20-14
=6 cm