複數,COMPLEX NUMBER 等待高手解答,等待只因渴求!

2007-01-03 8:59 am
解方程﹕
| z - 1| - z¯ = z^2 – 3z + 9 + 4i

為了清晰,簡單解釋一下﹕
i為虛數單位,z為未知數。絕對值裏面的是 z-1 。由於技術不好,所以第二個z上面的橫線偏右了,原題目的第二個z上有一橫線,稱為z的共軛複數。 ^代表次方。
求z
注意﹕z是複數,形如a+bi 的形式
更新1:

這題應該是有解

回答 (1)

2007-01-09 11:23 pm
✔ 最佳答案
Please find my deductions below:

圖片參考:http://f7.yahoofs.com/users/458862c7mf9ddb2ca/f6cbscd/__sr_/1075scd.jpg?phAV0oFBF3KIkLLO

Now, let y = z – 1, then it simplifies to:

圖片參考:http://f7.yahoofs.com/users/458862c7mf9ddb2ca/f6cbscd/__sr_/e75escd.jpg?phAV0oFBSQDffYA1

Then denote y = a + bi where a and b are real values:

圖片參考:http://f7.yahoofs.com/users/458862c7mf9ddb2ca/f6cbscd/__sr_/7742scd.jpg?phAV0oFBOo36QRtc

Comparing the real and imaginary parts, we have:

圖片參考:http://f7.yahoofs.com/users/458862c7mf9ddb2ca/f6cbscd/__sr_/1554scd.jpg?phAV0oFBHi00wLQZ
.... (1)

圖片參考:http://f7.yahoofs.com/users/458862c7mf9ddb2ca/f6cbscd/__sr_/7459scd.jpg?phAV0oFBdITgqVWG
.... (2)
Sub (2) into (1), we have:

圖片參考:http://f7.yahoofs.com/users/458862c7mf9ddb2ca/f6cbscd/__sr_/2c03scd.jpg?phAV0oFBtKQaKCkP

After expanding the equation, we have:

圖片參考:http://f7.yahoofs.com/users/458862c7mf9ddb2ca/f6cbscd/__sr_/16a2scd.jpg?phAV0oFBjt.icLMx


which is a polynomial equation of b of degree 8.
By using numerical approximation methods for roots like Newton’s or bisection method, we can obtain one of the root for (*) is b = 2.3755 (corr. to 4 d.p.).
Sub this result into (2), we get a = 0.1581 (corr. to 4 d.p.).
Therefore, y = 0.1581 + 2.3755 i
With z – 1 = y, we have z = 1.1581 + 2.3755 i.
Direct substitution of z to the original equation can yield the result.
It is worth to note that according to (*), there may be at most 8 possible values of b (and hence a). So to speak, other 7 possible solutions may be obtained through solving for the remaining 7 roots of (*) (if exist).

2007-01-09 16:23:09 補充:
(*) is the polynomial equation of b of degree 8.
參考: My Maths knowledge


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