Tam giác

H

hientamkute

H

hien_vuthithanh

1.kẻ $DH ,CK$ là 2 đường cao của hình thang cân $\rightarrow AH=BK=\dfrac{AB-CD}{2}=8 \rightarrow AK=18$

Xét $\Delta ACK$ ~ $\Delta CBK \rightarrow CK^2=AK.KB \rightarrow CK$

$\rightarrow S_{ABCD}=\dfrac{1}{2}(AB+CD).CK=...$


2.Xét $\Delta ABH $ ~ $\Delta CBA$ do: $\widehat{B}$ : chung , $\dfrac{AB}{BC}=\dfrac{BH}{AB}$

$\rightarrow \widehat{AHB}=\widehat{BAC}\rightarrow \widehat{BAC}=90^o$
 
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