好簡單代數(5點)

👨🏻‍🏫 學術台數學

[匿名]

2013-01-06 5:47 pm

30/x-3 - 30/x=2/3

回答 (4)

胡雪8°

2013-01-06 7:34 pm

✔ 最佳答案

[30 / (x - 3)] - (30 / x) = 2 / 3
[30x / x(x-3)] - [30(x - 3) / x(x - 3)] = 2 / 3
[30x - 30(x - 3)] / x(x - 3) = 2 / 3
(30x - 30x + 90) / (x² - 3x) = 2 / 3
90 / (x² - 3x) = 2 / 3
2(x² - 3x) = 3(90)
x² - 3x = 135
x² - 3x - 135 = 0
x = [3 ± √(3² + 4*135)] / 2
x = (3 + 3√61) / 2 或 x =(3 - 3√61) / 2

參考: 胡雪

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※Tony Cheung※

2013-01-06 8:15 pm

但是答案的確如此！不就是你打錯問題

(30/x-3)-(30/x)=2/3
90/(x^2-3x) = 2/3
(x^2-3x)/45 = 3
(1/45)x^2 - (1/15)x -3 =0

x = 13.2 or x = -10.2 (Correct to 3 sig. fig)

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