如图在△ABC中,AB=AC=9,∠BAD=120°,AD是△ABC的中线,AE是∠BAD的角平

如图在△ABC中,AB=AC=9,∠BAD=120°,AD是△ABC的中线,AE是∠BAD的角平分线,DFABAE的延长线于点F,求DF的长。

 


答案

解:∵AB=ACD为底边的中点,
ADBC,∠BAD=CAD.
∵∠BAC=120°
∴∠BAD=60°,∠ADB=90°.2分)
AE是∠BAD的角平分线,
∴∠DAE=EAB=30°
DFAB
∴∠F=BAE=30°
∴∠DAF=F=30°
AD=DF          4分)
AB=9,∠B=30°
AD=4.5
DF=4.5           6分)

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