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1

P

Q

abP

Q

P

Q

(R)

AB BC CA

A'B' B'C' C'A '

P

Q

R

AA'

B B'

CC'

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l:

' ' ' ' ' '

1 2 2 1 2 3 3 2 n 1 1 nA A A A , A A A A , ..., A A A A

' ' '

1 2 n 1 2 nA A ...A , A A ...A

' ' '

1 2 n 1 2 nA A ...A .A A ...A .

A1A2 A3

A4A5

'1

A

'2

A'3

A

'4

A

'5

A

1A2An,

1,

SA2, SAn .

v

1A2An

' ' '

1 2 nA ,A ...., A

' ' '

1 2 nA ,A ...., A

' ' ' ' ' '

1 2 2 1 2 3 3 2 n 1 1 nA A A A , A A A A , ...A A A A

S

A'

B'C'

D'

A

B C

D

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2

TOPPER. Ch

trong (P).

VD1: 1, G2 v G31G2G3) // (BCD).

= HD

A

B

C

D

I J

K

G1 G2

G3

Ko di AG1 BC = I, AG2 CD = J,

AG3 BD = K.

Trong tam gic AIJ, ta c:

1 2AG AG 2

.AI AJ 3

G1G2 // IJ

32AGAG

AJ AKG1G3 // KJ G2G3 // (BCD) (2).

IJ (BCD) G1G2 // (BCD) (1)

1G2 G2G3 = G2 (G1G2G3) // (BCD)

1

(OMN) // (SBC).

2khc nhau.

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VD2:

= HD

S

A

B C

ED M

QP

OI

N

V (P) // (SBD) nn (P) // BD

MN = (P) (ABCE)

(P) (SAE) = QM

(P) (SBC) = PN.

(P) (SCE) = PQ.

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VD3: 1, G2 v G3

1G2G3).

= HD

A

B

C

D

I J

K

G1 G2

G3M

N

P

(G1G2G3) // (BCD).

1

1G2G3) (ABC) = MN.

2

NP // BD NP // (BCD)

(G1G2G3) (ACD) = NP

(G1G2G3) (ABD) = MP

3

4

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VD4:

A

B

C

Q

P M

N

C'A'

B'

= HD

(A 'MN) (BCC'B') MN

(A 'MN) (ABC) MP

(A 'MN) (ABB'A ') PA '

(A 'MN) (ACC'A ') A 'N

5

(MNP).

6

7

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3

5

6

71 d1 AB = I

2 d2 A'C' = J