Parallélogramme quelconque

AB
C
D
A B
C
D
I
ABCD I [AC] [BD]
ABCD
(AB) (CD)I
(AB)//(CD) (BC)//(AD)
EF GH O [EG]O
[F H]
(EF )//(GH)O[EG] (EF )
(GH)O F
O(GH)
(F G) (EH)O
F O (EH)
F O
(GH) (EH)H O [F H]

AB
C
D
ABCD I
AB =CD BC =AD
ABCD
[AB] [CD]I
AB =CD BC =AD
EF GH EF =GH F G =EH O
[EG]EF GH
EF =GH O [EG]F
O G GH
F G =EH O [EG]F
E EH
F O
(EG)F H
O[F H]
EF GH
AB
C
D

ABCD I
d
BAD =
d
BCD
d
ABC =
d
ADC
ABCD
d
BAD
d
BCD I
d
BAD =
d
BCD
d
ABC =
d
ADC
AB
C
D
ABCD (AB)//(CD)AB =CD
I[AC]ABCD
(AB)//(CD)I[AC] (AB) (CD)
I B I
(CD)
AB =CD I [AC]B
I C CD
B I
(CD) (AC)B D
I[BD]
ABCD