c*********o
发帖数: 8367 | 1 【 以下文字转载自 WaterWorld 讨论区 】
发信人: sweetlife (甜蜜生活), 信区: WaterWorld
标 题: 大家看看我错在哪里？
发信站: BBS 未名空间站 (Tue Jul 2 17:40:17 2013, 美东)
square root of -36 is 6i
square root of -4 is 2i
square root of -36 times square root of -4 is square root of -36x-4=144,
which is 12.
but 6ix2i=-12. So I proved 12=-12. |
l*********m
发帖数: 16971 | 2 文科生
【在 c*********o 的大作中提到】
: 【 以下文字转载自 WaterWorld 讨论区 】
: 发信人: sweetlife (甜蜜生活), 信区: WaterWorld
: 标 题: 大家看看我错在哪里？
: 发信站: BBS 未名空间站 (Tue Jul 2 17:40:17 2013, 美东)
: square root of -36 is 6i
: square root of -4 is 2i
: square root of -36 times square root of -4 is square root of -36x-4=144,
: which is 12.
: but 6ix2i=-12. So I proved 12=-12.
|
k**********4
发帖数: 16092 | 3 sb
【在 c*********o 的大作中提到】
: 【 以下文字转载自 WaterWorld 讨论区 】
: 发信人: sweetlife (甜蜜生活), 信区: WaterWorld
: 标 题: 大家看看我错在哪里？
: 发信站: BBS 未名空间站 (Tue Jul 2 17:40:17 2013, 美东)
: square root of -36 is 6i
: square root of -4 is 2i
: square root of -36 times square root of -4 is square root of -36x-4=144,
: which is 12.
: but 6ix2i=-12. So I proved 12=-12.
|
a*****1
发帖数: 3134 | 4 -36*-4=144
square root on left side is not an allowed operation.
【在 c*********o 的大作中提到】
: 【 以下文字转载自 WaterWorld 讨论区 】
: 发信人: sweetlife (甜蜜生活), 信区: WaterWorld
: 标 题: 大家看看我错在哪里？
: 发信站: BBS 未名空间站 (Tue Jul 2 17:40:17 2013, 美东)
: square root of -36 is 6i
: square root of -4 is 2i
: square root of -36 times square root of -4 is square root of -36x-4=144,
: which is 12.
: but 6ix2i=-12. So I proved 12=-12.
|
t*********3
发帖数: 4304 | 5 lol，又一个文科生。
【在 a*****1 的大作中提到】
: -36*-4=144
: square root on left side is not an allowed operation.
|
m**2
发帖数: 66 | 6 Strictly speaking, square root of -36 could be 6i or -6i. So when you say it
is 6i, actually you have chose a particular branch of the solution, which
is 6i. Similarly for 4i as the square root of -16.
So if you do not choose branches of square roots very carefully, then square
root of -36 times square root of -4 may not be square root of (-36)*(-4),
as you see from the obvious contradiction.
This phenomenon does not exist for real numbers. |
X*********r
发帖数: 11803 | 7 大牛厉害。lol
★ 发自iPhone App: ChineseWeb 7.8
【在 c*********o 的大作中提到】
: 【 以下文字转载自 WaterWorld 讨论区 】
: 发信人: sweetlife (甜蜜生活), 信区: WaterWorld
: 标 题: 大家看看我错在哪里？
: 发信站: BBS 未名空间站 (Tue Jul 2 17:40:17 2013, 美东)
: square root of -36 is 6i
: square root of -4 is 2i
: square root of -36 times square root of -4 is square root of -36x-4=144,
: which is 12.
: but 6ix2i=-12. So I proved 12=-12.
|
