✔ 最佳答案
1.
答案:(D)沒有實數解
y = x² + 3 ...... [1]
y = 2x - (1/2) ...... [2]
[1] = [2] :
x² + 3 = 2x - (1/2)
2x² + 6 = 4x - 1
2x² - 4x + 7 = 0
判別式 Δ
= (-4)² - 4x2x7
= 16 - 56
= -40 < 0
由於判別式 Δ < 0,方程式無實數解。
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9.
答案:四個選擇無一正確
若 ∠ACB 為 ∠ACO之誤,則答案為: B. 20°
若 ∠ACB 為 ∠ABO之誤,則答案為: C. 30°
OB = OC (同圓半徑)
∠OBC = ∠OCB = 40° (等腰Δ兩底角)
在 ΔOBC 中:
∠BOC + ∠OBC + ∠OCB = 180°
∠BOC + 40° + 40° = 180°
∠BOC = 100°
∠BOC 及 ∠BAC分別為對同弧之圓心角及圓周角。
∠BAC = 100° ÷ 2 = 50°
在 ΔABC 中:
∠BAC + ∠ABC + ∠ACB = 180°
50° + 70° + ∠ACB = 180°
∠ACB = 60°
(四選擇中無一正確)
∠ACO = ∠ACB - ∠OCB = 60° - 40° = 20°
∠ABO = ∠ABC - ∠OBC = 70° - 40° = 30°