JJ138求确定~

fengchen318 · 发表于 2011-4-9 16:36:33

101、(DS)x的值是什么？
（1）(x^2-25)^(1/2)=x-5
（2）(25-x^2)^(1/2)=x-5
（没记错的话应该就是这样）

条件一，（x-5）（x+5）=(x-5)^2

所以x=5.

条件二，（5-x）(5+x)=（x-5）^2.

X=5或者x=0.但是X-5>=0,所以x不等于0

选D。

条件二我算的是5-x>=0,所以x≤5，得不出来。。。。我选A

sdcar2010 · 发表于 2011-4-9 21:05:50

LZ, If a number's square root is (x-5), then (x-5) is equal to or greater than zero. x-5>=0.

DDDDDDDDDDDDDd

fengchen318 · 发表于 2011-4-9 21:16:28

LZ, If a number's square root is (x-5), then (x-5) is equal or greater than zero. x-5>=0.

DDDDDDDDDDDDDd

-- by 会员 sdcar2010 (2011/4/9 21:05:50)

啊，对~我脑子坏了。。。谢谢你。。。

leci · 发表于 2011-4-10 22:05:40

LZ, If a number's square root is (x-5), then (x-5) is equal to or greater than zero. x-5>=0.

DDDDDDDDDDDDDd

-- by 会员 sdcar2010 (2011/4/9 21:05:50)

完了完了，我糊涂了，平方根必须得是正数吗？负数不行吗？
呼唤CDCAR!!!!

sdcar2010 · 发表于 2011-4-10 22:34:34

LZ, If a number's square root is (x-5), then (x-5) is equal to or greater than zero. x-5>=0.

DDDDDDDDDDDDDd

-- by 会员 sdcar2010 (2011/4/9 21:05:50)

完了完了，我糊涂了，平方根必须得是正数吗？负数不行吗？
呼唤CDCAR!!!!

-- by 会员 leci (2011/4/10 22:05:40)

Sorry about the confusion.

If you write
(a)^(1/2) = b
then b>0.

If you write
- (a)^(1/2) = b
then b<0.

However, (-b)^2 =b^2 = a; and both b and -b are the square root of a.

leci · 发表于 2011-4-10 23:05:06

LZ, If a number's square root is (x-5), then (x-5) is equal to or greater than zero. x-5>=0.

DDDDDDDDDDDDDd

-- by 会员 sdcar2010 (2011/4/9 21:05:50)

完了完了，我糊涂了，平方根必须得是正数吗？负数不行吗？
呼唤CDCAR!!!!

-- by 会员 leci (2011/4/10 22:05:40)

Sorry about the confusion.

If you write
(a)^(1/2) = b
then b>0.

If you write
- (a)^(1/2) = b
then b<0.

However, (-b)^2 =b^2 = a; and both b and -b are the square root of a.

-- by 会员 sdcar2010 (2011/4/10 22:34:34)

感谢，但还是糊涂。
难道是我的基础知识出了问题？
简单说吧，请问，4^（1/2）难道不是2和-2吗？

sdcar2010 · 发表于 2011-4-11 00:39:30

LZ, If a number's square root is (x-5), then (x-5) is equal to or greater than zero. x-5>=0.

DDDDDDDDDDDDDd

-- by 会员 sdcar2010 (2011/4/9 21:05:50)

完了完了，我糊涂了，平方根必须得是正数吗？负数不行吗？
呼唤CDCAR!!!!

-- by 会员 leci (2011/4/10 22:05:40)

Sorry about the confusion.

If you write
(a)^(1/2) = b
then b>0.

If you write
- (a)^(1/2) = b
then b<0.

However, (-b)^2 =b^2 = a; and both b and -b are the square root of a.

-- by 会员 sdcar2010 (2011/4/10 22:34:34)

感谢，但还是糊涂。
难道是我的基础知识出了问题？
简单说吧，请问，4^（1/2）难道不是2和-2吗？

-- by 会员 leci (2011/4/10 23:05:06)

I would go with 2. Gen Hao 2 is 1.414, not -1.414.

JJ138求确定~

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