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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