如图,AB=AC,AD=BD,CB=CD,求∠ABC的度数

来源:学生作业帮助网 编辑:六六作业网 时间:2024/11/26 11:22:23
如图,AB=AC,AD=BD,CB=CD,求∠ABC的度数如图,AB=AC,AD=BD,CB=CD,求∠ABC的度数如图,AB=AC,AD=BD,CB=CD,求∠ABC的度数∵CB=CD∴∠CBD=∠

如图,AB=AC,AD=BD,CB=CD,求∠ABC的度数
如图,AB=AC,AD=BD,CB=CD,求∠ABC的度数

如图,AB=AC,AD=BD,CB=CD,求∠ABC的度数
∵CB=CD
∴∠CBD=∠CDB
∵AD=BD
∴∠A=∠DBA
∵AB=AC
∴∠ABC=∠C
∵∠CDB=∠A+∠DBA=2∠A
∴∠ABC=∠DBA+∠CBD=∠A+2∠A=3∠A
∴∠ACB=∠ABC=3∠A
∵∠A+∠ABC+∠ACB=180°
∴∠A+3∠A+3∠A=180°
∠A=180°/7
∴∠ABC=3∠A=540°/7

由CB=CD得:∠C=∠BDC,由AD=BD得:∠A=∠ABD,因为∠BDC=∠A+∠ABD,
所以:∠C=2∠A,又AB=AC,所以∠ABC=∠C=2∠A,由于∠A+∠ABC+∠ACB=180°,
所以5∠A=180°,∠A=36°,故∠ABC=2∠A=72°