设 DB = X
则 AB = 3X.DC = 5X.
因为 E.F 分别为 AB ,CD 中点
所以 EB = 1/2 AB = 1/2 × 3X
DF = 1/2DC = 1/2 × 5X
EF = ED + DF
= ( EB - DB ) + DF
= ( 1/2 × 3X -- X ) + 1/2 × 5X
= 3X
因为 EF = 6cm
所以 3X= 6
所以 X = 2
所以 AB = 3X = 6cm
CD = 5X = 10cm.
设 DB = X
则 AB = 3X.DC = 5X.
因为 E.F 分别为 AB ,CD 中点
所以 EB = 1/2 AB = 1/2 × 3X
DF = 1/2DC = 1/2 × 5X
EF = ED + DF
= ( EB - DB ) + DF
= ( 1/2 × 3X -- X ) + 1/2 × 5X
= 3X
因为 EF = 6cm
所以 3X= 6
所以 X = 2
所以 AB = 3X = 6cm
CD = 5X = 10cm.