諗爆頭的數學題~教教我~20點

1.
r = [3+sqrt(29)] / 2 or [3-sqrt(29)] / 2
r^2 = [38+sqrt(29)] / 4 or [38-sqrt(29)] / 4

r^5 - 3r^4 - 5r^3 + 5r^2 - 6r
= r[(r^4 - 5r^2 - 6) - 3r^3 - 5r]
= r[(r^2 - 6)(r^2 + 1) - r(3r^2 - 5)]
substitute r and r^2
when r = [3+sqrt(29)] / 2
finally you get (1/2)[1753+321sqrt(29)]
when r = [3-sqrt(29)] / 2
finally you get .......

2.
selling price to Ming = 120000 (1+r) = A
selling price from Ming = A (1+r) = 120000 (1+r)^2
overall: 120000 (1+r)^2 - 120000 (1+r) = 28800
(1+r)^2 - (1+r) = 0.24
(1+r)^2 - (1+r) + 1/4 = 0.24 + 1/4
[(1+r) - 1/2]^2 = 0.24 + 1/4 = 0.49
0.5 + r = 0.7 => r = 0.2 = 20%

3.
Let x and y be the speed of Ming and me respectively
distance between = 60m at 0s
distance between = 2 x 27m at 6s later
we travel 6m in 6s towards each other
x + y = 1
2 = y - x
=> y = 1.5, x = -0.5 => contradicts to the question as x < 0, Ming moved away from the bus stop.

4.
let a be the positive root, and such that -a be the negative root
product of root: (a)(-a) = c => c < 0

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因為我之前有拿我的手機去那周轉過

他們服務很好 人又親切 裡面燈光明亮

重點是 我拿手機去周轉 他們小心翼翼的幫我包起來

讓我好放心 還拿信封袋封口 妥善保管我的手機

好貼心的服務 你可以先打電話去諮詢

或直接去諮詢 滿意在借 老闆人非常好

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