,
1. . , .
, .
.
.
AB ∥CD, BC∥AD
AB = CD; BC = AD
.
AC ⊥ BD
, .
, △ BOC =△ DOC (BO = OD, OC , BC = CD). , ∠ BOC =∠ COD, .
⇒∠ BOC =90∘ ∠ COD =90∘.
.
AC =2⋅ AO =2⋅ CO
BD =2⋅ BO =2⋅ DO
.
∠1=∠2; ∠5=∠6;
∠3=∠4; ∠7=∠8.
, , , 4 :
△ BOC, △ BOA, △ AOD, △ COD.
, BD, AC .
4 .
.
AC 2+ BD 2=4⋅ AB 2
.
AC ⊥ BD
ABCD , ABCD⇒ ABCD .
ABCD ⇒ AO = CO; BO = OD. , AC AC ⊥ BD ⇒△ AOB =△ BOC =△ COD =△ AOD - 2- .
, AB = BC = CD = AD
!
( ) , .
∠ A =∠ C, ABCD . AC ∠ A ∠ C.
, △ ABC =△ ADC .
, AB = BC = CD = DA, ABCD .
: () .
:
, .
. , ,
1. . , .
. .
|
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2.
1. .
AB = CD, BC = AD
2. 90.
3. , .
4. , , , 180.
5. .
△ ABC =△ ACD, △ ABD =△ BCD