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13 a 已做 ，答案是13 分43 十 13 分124，但13B 就不識了，求解答

top11 2021-3-23 22:05

[quote]原帖由 [i]Dplease[/i] 於 2021-3-23 01:14 PM 發表 [url=https://www.discuss.com.hk/redirect.php?goto=findpost&pid=533243808&ptid=29788079][img]https://www.discuss.com.hk/images/common/back.gif[/img][/url]
13 a 已做 ，答案是13 分43 十 13 分124，但13B 就不識了，求解答 [/quote]
13(a)
(1 + 2i)/(2 - 3i) - 3(1 - 3i)
= (1 + 2i)(2 + 3i)/[(2 - 3i)(2 + 3i)] - 3(1 - 3i)
= (2 + 3i + 4i - 6)/(4 + 9) - 3 + 9i
= (-4 + 7i)/13 - 3 + 9i
= (-4/13 - 3) + (7/13 + 9)i
= -43/13 + 124/13 i

13(b)
(1 + 2i)/(2 - 3i) - 3(1 - 3i) = x + 3i - 5(2 - 3yi)
By (a),
-43/13 + 124/13 i = (x - 10) + (3 + 15y)i
By comparing the real part and the imaginary part,
{ x - 10 = -43/13
{ 3 + 15y = 124/13

{ x = 87/13
{ y = 17/39

[quote]原帖由 [i]top11[/i] 於 2021-3-23 10:05 PM 發表 [url=https://www.discuss.com.hk/redirect.php?goto=findpost&pid=533263846&ptid=29788079][img]https://www.discuss.com.hk/images/common/back.gif[/img][/url]

13(a)
(1 + 2i)/(2 - 3i) - 3(1 - 3i)
= (1 + 2i)(2 + 3i)/[(2 - 3i)(2 + 3i)] - 3(1 - 3i)
= (2 + 3i + 4i - 6)/(4 + 9) - 3 + 9i
= (-4 + 7i)/13 - 3 + 9i
= (-4/13 - 3) + (7/13 + 9)i
= -43/13 + 124/13 ... [/quote]

X 求到，但Y 求不到你所講嘅答案

top11 2021-3-24 14:18

[quote]原帖由 [i]Dplease[/i] 於 2021-3-24 12:05 PM 發表 [url=https://www.discuss.com.hk/redirect.php?goto=findpost&pid=533280812&ptid=29788079][img]https://www.discuss.com.hk/images/common/back.gif[/img][/url]

X 求到，但Y 求不到你所講嘅答案 [/quote]

[quote]原帖由 [i]top11[/i] 於 2021-3-24 02:18 PM 發表 [url=https://www.discuss.com.hk/redirect.php?goto=findpost&pid=533285614&ptid=29788079][img]https://www.discuss.com.hk/images/common/back.gif[/img][/url]

top11 2021-3-24 16:55

[quote]原帖由 [i]Dplease[/i] 於 2021-3-24 04:36 PM 發表 [url=https://www.discuss.com.hk/redirect.php?goto=findpost&pid=533291689&ptid=29788079][img]https://www.discuss.com.hk/images/common/back.gif[/img][/url]

3 + 15y = 124/13

15y = 124/13 - 3

15y = 124/13 - 39/13

15y = (124 - 39)/13

15y = 85/13

3y = 17/13

y = 17/39

ttkwan 2021-3-28 23:22

[quote]原帖由 [i]Dplease[/i] 於 2021-3-23 01:14 PM 發表 [url=https://www.discuss.com.hk/redirect.php?goto=findpost&pid=533243808&ptid=29788079][img]https://www.discuss.com.hk/images/common/back.gif[/img][/url]
13 a 已做 ，答案是13 分43 十 13 分124，但13B 就不識了，求解答 [/quote]

13a計完樓主心驚所以怕咗13b

ttkwan 2021-3-28 23:32

[quote]原帖由 [i]ttkwan[/i] 於 2021-3-28 11:22 PM 發表 [url=https://www.discuss.com.hk/redirect.php?goto=findpost&pid=533473549&ptid=29788079][img]https://www.discuss.com.hk/images/common/back.gif[/img][/url]

13a計完樓主心驚所以怕咗13b