C 11
22, 2016
5 4 3 2 1 2
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A, B, C, D . AB, BC, CD, DA . ∠DAB, ∠ABC, ∠BCD, ∠CDA , ∠A, ∠B, ∠C, ∠D . . AC, BD .
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. (AB, BC), (BC, CD), (CD, DA), (DA, AB) ABCD .
� . � ABCD AD, BC , 180°. � AB ∥ DC AD, BC , . AD, BC . � E, F EF = (AB+CD)/2 � � . � . � . � 4
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a, b. h h/2(a+b)
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. (AB, DC), (AD, BC) .
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d. a, b. = d/2(a+b)
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90° . , . AB ∥ DC, AD ∥ BC ∠A = ∠B = ∠C = ∠D = 90°.
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b, h = bh
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d, D = dD/2 a h ah
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90° .
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AB ∥ DC and AD ∥ BC � , � , � 180° � . � . � 3 �
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l, b = lb = 2(l+b)
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. � 360° � 3 � 4, 3 � � 5
. AB ∥ DC, AD ∥ BC AB = BC = CD = DA.
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AB ∥ DC, AD ∥ BC, AB = BC = CD = DA ∠A = ∠B = ∠ C = ∠D = 90°. � , ( ) � . � . � � . � 4 . � . � 1 � , . � , .
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d =(dxd)/2 d a d=m 2 a=m, d=m a = (m/2)2