Choosen As Best Answer

1.
(1)
∠ADE = ∠CDE
又 AB 平行 CD
=> ∠AED = ∠CDE (內錯角)
=> ∠ADE = ∠AED => AD = AE
(2)
假設 AE = x => AB = x+3 = CD
AE = AD = x = DE = BC
2*(x+3) + x + x = 30
2x +6 +2x = 30
4x = 24
x = 6 => 梯形周長 = 3 + (3+6) +6 +6 = 24

2.
(1)
兩條對角線相互平分 => 平行四邊形
(2)
OA = OC = 2、OB = 4、∠AOD = ∠BOC = 60度、∠OCB = 90度(切線)
=> BC = 2√3
△ABC為直角三角形 = 1/2 * ABCD面積
△ABC = 1/2 * 2√3 * 4 = 4√3
=> ABCD面積 = 4√3 * 2 = 8√3

Balm of Gilead

3.
如圖
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