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# 北师大数学七年级下册 - PowerPoint PPT Presentation

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### 北师大数学七年级下册

5.3 简单的轴对称图形

——角平分线性质的运用

F

F

A

D

E

P

C

O

B

△ CDO≌ △ CEO（AAS）

CD=CE（全等三角形的对应边相等）

A

D

E

P

C

O

B

∵ ∠1= ∠2,CD ⊥OA ，CE ⊥OB

∴CD=CE(角的平分线上的点到这个角的两边的距离相等)

1

2

A

A

E

E

O

O

D

D

B

B

P

P

1

C

C

2

CD⊥AO,CE⊥BO

A

A

O

O

D

D

B

B

P

P

3

C

C

1

1

4

2

2

E

E

E

A

D

D

C

B

A

C

B

1、如图，在Rt△ABC中，BD是∠ABC的平分线，DE⊥AB，垂足为E，DC＝5，求DE的长。

A

O

B

D

P

C

F

E

1、OP是∠ABC的平分线， CD ⊥OA， CE ⊥OB

→CD=CE

2、证明△CDF≌△CEF,得到DF=FE