题目内容
如图,在?ABCD中,AB=6,AD=9,∠BAD的平分线交BC于点E,交DC的延长线于点F,BG⊥AE,垂足为G,若BG=
,则△CEF的面积是( )
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A.![]() | B.![]() | C.![]() | D.![]() |
A
首先,由于AE平分∠BAD,那么∠BAE=∠DAE,由AD∥BC,可得内错角∠DAE=∠BEA,等量代换后可证得AB=BE,即△ABE为等腰三角形,根据等腰三角形“三线合一”的性质得出AE=2AG,而在Rt△ABG中,由勾股定理可求得AG的值,即可求得AE的长;然后,证明△ABE∽△FCE,再分别求出△ABE的面积,然后根据面积比等于相似比的平方即可得到答案.
解:∵AE平分∠BAD,
∴∠DAE=∠BAE;
又∵四边形ABCD是平行四边形,
∴AD∥BC,
∴∠BEA=∠DAE=∠BAE,
∴AB=BE=6,
∵BG⊥AE,垂足为G,
∴AE=2AG.
在Rt△ABG中,∵∠AGB=90°,AB=6,BG=
,
∴AG=
=2,
∴AE=2AG=4;
∴S△ABE=
AE•BG=
×4×
=
.
∵BE=6,BC=AD=9,
∴CE=BC﹣BE=9﹣6=3,
∴BE:CE=6:3=2:1.
∵AB∥FC,
∴△ABE∽△FCE,
∴S△ABE:S△CEF=(BE:CE)2=4:1,
则S△CEF=
S△ABE=
故选A.
解:∵AE平分∠BAD,
∴∠DAE=∠BAE;
又∵四边形ABCD是平行四边形,
∴AD∥BC,
∴∠BEA=∠DAE=∠BAE,
∴AB=BE=6,
∵BG⊥AE,垂足为G,
∴AE=2AG.
在Rt△ABG中,∵∠AGB=90°,AB=6,BG=

∴AG=

∴AE=2AG=4;
∴S△ABE=
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
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∵BE=6,BC=AD=9,
∴CE=BC﹣BE=9﹣6=3,
∴BE:CE=6:3=2:1.
∵AB∥FC,
∴△ABE∽△FCE,
∴S△ABE:S△CEF=(BE:CE)2=4:1,
则S△CEF=

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故选A.
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