toán khó

H

huynhbachkhoa23

Bài làm:

Kẻ $FF' // BC\;\;\;(F' \in AB)$

$\widehat{BF'D}=\widehat{CFD}=180^{o}-\widehat{FCD}-\widehat{FDC}=180^{o}-\widehat{FDC}-\widehat{FDE}=\widehat{EDB}$

$\rightarrow \Delta BDE \sim \Delta BF'D$

$\rightarrow \mathfrak{dpcm}$
 
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