过点A作AE‖DB交CB的延长线于点E,过A作AH⊥BC于点H∵AD‖EB,AE‖DB,∴四边形AEBD是平行四边形,∴EA=BD在直角△AHC中,∠ACH=30°,∴AH=AC÷2=4.5∵AD‖BC,∴∠CBD=∠ADB=45°,∵AE‖DB,∴∠E=∠CBD=45°在直角△AHE中...