中三-四邊形20點

(a). 因為 AB = DC, ∠BAF = ∠CDG = 90° (正方形)
又 AF = DG
所以 △FAB = △GDC

(b). 因為 △FAB = △GDC
所以 ∠ABF = ∠DCG
而 ∠ABC = ∠DCB = 90°
所以 ∠EBC = ∠ECB
△EBC 是等腰三角形

(a)<DAB = <ADC = <90,
AF = GD,
AB = CD,
FB = GC

(b)<ABF + <FBC = <90,
<DCG + <GCB = <90,
<ABF = <DCG,
<FBC = <GCB

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