✔ 最佳答案
1.
∠R + 優角∠P= 360° (同頂角)
∠R + (8r + 20°) = 360°
∠R = 340° ‒ 8r
∠P + ∠Q + ∠R = 180° (三角形內角和)
(r + 20°) + (2r ‒ 10°) + (340° ‒ 8r) = 180°
r + 20° + 2r ‒ 10° + 340° ‒ 8r = 180°
350° ‒ 5r = 180°
5r = 170°
r = 34°
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2.
連 BD 及 BE。
ΔABE內角和 + Δ內角和 + Δ內角和 = 180° × 3
五邊形ABCDE內角和 = 540°
50° + (360° ‒ x) + 20° + (360° ‒ 170°) + 20° = 540°
50° + 360° ‒ x + 20° + 360° ‒ 170° + 20° = 540°
640° ‒ x = 540°
x = 100°
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3.
多邊形外角和 = 360°
∠PUV + ∠QVW + ∠RWX + ∠SXY + ∠TYU = 360°
∠PVU + ∠QWV + ∠RXW + ∠SYX + ∠TUY = 360°
ΔPUV內角和: ∠PUV + ∠PVW + a = 180° ......[1]
ΔQVW內角和: ∠QVW + ∠QWV + e = 180° ...... [2]
ΔRWX內角和: ∠RWX + ∠RWX + d = 180° ...... [3]
ΔSXY內角和: ∠SXY + ∠SYX + c = 180° ...... [4]
ΔTYU內角和: ∠TYU + ∠TUY + b = 180° ...... [5]
[1] + [2] + [3] + [4] + [5] :
(∠PUV + ∠QVW + ∠RWX + ∠SXY + ∠TYU) + (∠PVU + ∠QWV + ∠RXW + ∠SYX + ∠TUY) + (a +b + c + d + e) = 180° × 5
360° + 360° + (a + b + c + d + e) = 900°
720° + (a + b + c + d + e) = 900°
a + b + c + d + e = 180°
2015-06-14 20:57:46 補充:
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2015-06-15 10:47:33 補充:
2.
應為:
「ΔABE內角和 + ΔBDE內角和 + ΔCBD內角和 = 180° × 3」
「五邊形ABCDE內角和 = 540°」
亦可用公式:多邊形內角和 = (n ‒ 2) × 180°
所以,五邊形ABCDE內角和 = (5 ‒ 2) × 180° = 540°
2015-06-17 10:32:24 補充:
3. 另解:
∠PUV 是 ΔUSQ 的外角: ∠PUV = c + e
∠PVU 是 ΔVTR 的外角: ∠PVU = b + d
ΔPUV 的內角和: ∠PUV + ∠PVU + a = 180°
(c + e) + (b + d) + a = 180°
a + b + c + d + e = 180°