CD=1/3BC=1/3×1/3AB=1/9AB
DE=1/3CD=1/3×1/9AB=1/27AB
∴AE=AB+BC+CD+DE=AB+1/3AB+1/9AB+1/27AB=38/27AB
∴AB=80÷38/27=80×27/38=1080/19厘米
CD=1/3BC=1/3×1/3AB=1/9AB
DE=1/3CD=1/3×1/9AB=1/27AB
∴AE=AB+BC+CD+DE=AB+1/3AB+1/9AB+1/27AB=38/27AB
∴AB=80÷38/27=80×27/38=1080/19厘米