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# 三垂线定理 - PowerPoint PPT Presentation

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## 三垂线定理

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Presentation Transcript

l

D1

C1

M

A1

B1

D

C

A

B

P

A

O

a

P

A

O

a

AO是PA在平面 内的射

P

A

C

O

B

P

A

C

O

B

（1）PA⊥BC，PC⊥AB，PB ⊥ AC.

（2）A在面PBC内的射影也是△PBC的垂心.

PB，PC在平面ABC上的射影，

∵O是△ ABC的垂心，

∴OA⊥BC，于是PA⊥BC，

P

A

C

O

B

(A)外心(B)内心 (C)垂心 (D)重心

A

H

P

C

B

A

H

P

C

B

P

F

E

C

A

B

E、F.

P

D

A

C

B

E

PA⊥平面ABCD ，在BC边上是否存在点E，

P

N

A

D

M

B

C

1.《课本》P25 6

2.《课时训练》P25 三. 1

3.《教学测试》P210 8