Yorty4
幼苗
共回答了14个问题采纳率：92.9% 举报
设AD∥BC
AB=AD=DC
BD=BC
求∠A,∠ABC
∵AD∥BC
∴∠ADB=∠CBD
∵AD=AB
∴∠ADB=∠ABD
∴∠ABD=∠CBD=1/2∠ABC
∵AB=DC
∴∠ABC=∠C
∵BD=BC
∴∠C=∠BDC=2∠ABD=2∠ADB=2∠CBD
∵∠C+∠ADC=180°
∴∠ADB+2∠ADB+2∠ADB=180°
∠ADB=∠ABD=36°
∴∠ABC=2∠ABC=72°
∠A=180°-72°=108°
1年前
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