hyuj
春芽
共回答了21个问题采纳率:95.2% 举报
①证明:∵AB=AC,∠BAD=∠CAD∴∠ADC=90°,BD=CD(三线合一)∵AE平分∠FAC∴∠FAE=∠CAE∴∠CAD+∠CAE=1/2∠BAC+1/2∠FAC=90°即∠DAE=90°=∠ADB∴AE//BC∵DE//AB∴四边形ABDE是平行四边形∴AE=BD∴AE=CD∵AE//CD∴四边形AECD是平行四边形又∵∠ADC=90°∴四边形AECD是矩形②∵BD=CD=1/2BC=3 ∴AD=S四边形AECD÷CD=4AB=√(BD^2+AD^2)=5
1年前
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