✔ 最佳答案
1.
x(x - 1) - mx + (m + 1) = 0
x² - x - mx + (m + 1) = 0
x² - (m + 1) x + (m + 1) = 0
由於兩根相等,故此 判別式 Δ = 0
[-(m + 1)]² - 4(m + 1) = 0
m² + 2m + 1 - 4m - 4 = 0
m² - 2m - 3 = 0
(m + 1)(m - 3) = 0
m = -1 或 m = 3
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2.
25(1 - x%)² = 16
25(1 - 0.01x)² = 16
25(1 - 0.02x + 0.0001x²) = 16
0.0025x² - 0.5x + 9 = 0
x² - 200x + 3600 = 0
(x - 20)(x - 180) = 0
x = 20 或 x = 180 (不合)
另解:
25(1 - x%)² = 16
(1 - x%)² = 16/25
1 - x% = 4/5 或 1 - x = -4/5 (不合)
1 - x% = 80%
x = 20
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3.
設乙跑一圈要 m 分鐘。
則甲每分鐘跑 1/10 圈,而乙每分鐘跑 1/m 圈。
當相遇時,乙跑了的時間 = (m - 9) 分鐘
甲跑了的時間也是 (m - 9) 分鐘
於 (m - 9) 分鐘的時間,甲和乙共跑了一圈的長度。
(m - 9)(1/10) + (m - 9)(1/m) = 1
[(m - 9)/10] + [(m - 9)/m] = 1
[m(m - 9)/10m] + [10(m - 9)/10m] = (10m/10m)
m(m - 9) + 10(m - 9) = 10m
m² - 9m + 10m - 90 = 10m
m² - 9m - 90 = 0
(m - 15)(m + 6) = 0
m = 15 或 m = -6 (不合)
乙跑一圈需時 = 15 分鐘
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4.
(a + b) : a = a : b
a² = b(a + b)²
a² = ab + b²
a² - ab - b² =0
(a² - ab - b²)/b² = 0
(a/b)² - (a/b) - 1 = 0
a/b = [1 ± √(1² +4)]/2
a/b = (1 + √5)/2 或 a/b = (1 - √5)/2 (不合)
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5.
|x² - 3x - 10| = |x² +5x + 6|
x² - 3x - 10 = x² +5x + 6 或 x² - 3x - 10 = -(x² +5x + 6)
8x = -16 或 x² - 3x - 10 = -x² -5x - 6
x = -2 或 2x² + 2x- 4 = 0
x = -2 或 x² + x - 2 = 0
x = -2 或 (x + 2)(x - 1) = 0
x = -2 (重根) 或 x = 1