Extend the segment Ba to the point C, make BC = 3ba, take the midpoint D of BC, know ad = 2cm (as shown in the figure), and find the length of BC

Extend the segment Ba to the point C, make BC = 3ba, take the midpoint D of BC, know ad = 2cm (as shown in the figure), and find the length of BC

∵ BC = 3ba, the midpoint D of BC
∴BD=0.5BC=1.5AB
∵AD=2cm=BD-BA=1.5AB-AB=0.5AB
∴AB=4㎝
∴BC=3×4=12㎝