急! 急 ! F4 Quadratic Equations.

2011-10-13 12:37 am
請詳細教我計以下幾條 :


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回答 (1)

2011-10-13 12:56 am
✔ 最佳答案
20) Let x% be the dep. rate of the first year, then (x + 5)% will be the dep. rate of the second year. Hence:

300000 (1 - x/100) [1 - (x + 5)/100] = 180000

30 (100 - x) (95 - x) = 180000

x2 - 195x + 9500 = 6000

x2 - 195x + 3500 = 0

(x - 175)(x - 20) = 0

x = 175 (rej.) or 20

So the dep. rate of the first year is 20%.

21) Let the interest rate be x%, then:

[20000 (1 + x/100)2 - 20000] - 20000(2x/100) = 30

2(100 + x)2 - 20000 - 400x = 30

2x2 = 30

x = 3.87

So the interest rate is 3.87%

22) Let x% be the annual rate of the first half year, then (x + 1)% will be the rate of the second half year.

So:

1000000 (1 + x/200) [1 + (x + 1)/200] = 1035300

25 (200 + x)(201 + x) = 1035300

x2 + 401x + 40200 = 41412

x2 + 401x - 1212 = 0

(x + 404)(x - 3) = 0

x = -404 (rej.) or 3

Hence the annual interest rate for the first half year is 3%
參考: 原創答案


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