Infected Integers...

Algebra Level 3

Let z z be any integer, then what can be said about the inequality z z 2 \sqrt { z } \le \sqrt { { z }^{ 2 } } ?


AYWC?

The inequality is not always valid The inequality is always not valid I don't like integers The inequality is always valid

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2 solutions

It is true for z \ge 0, and not valid for z < 0.

The inequality does not make any sense for z < 0 z<0 .

If I were to ask the question as which of these is valid for integers z < 1 z<-1 with options as

A. z z 2 \sqrt{z} \leq \sqrt{z^2}

B. z z 2 \sqrt{z} \leq \sqrt{z^2}

C. z = z 2 \sqrt{z} = \sqrt{z^2}

Which is the correct option?

Can anyone help me on that?

Janardhanan Sivaramakrishnan - 6 years, 4 months ago

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none of the options

Soumo Mukherjee - 6 years, 4 months ago

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If it is'none of this', then it would mean that the relational operator has no meaning while dealing with complex numbers. 2 > 1 > 1 2>1>-1 . But, it is meaningless to say i < i -i<i or i < i i<-i .

The relationship z z 2 \sqrt{z} \leq \sqrt{z^2} is 'meaningless for z < 0 z<0 ', not invalid.

z 3 < z 3 3 \sqrt[3]{z} < \sqrt[3]{z^3} is invalid for z ( , 1 ) ( 0 , 1 ) z \in (-\infty,-1) \cup (0,1) because the inequality still makes sense in the said domain. But, the previous one does not.

Janardhanan Sivaramakrishnan - 6 years, 4 months ago

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@Janardhanan Sivaramakrishnan The complex numbers cannot be ordered. See this note for a reason.

It is not guaranteed that we can always compare 2 elements. This is only possible if the structure we are working with is totally ordered .

Calvin Lin Staff - 6 years, 4 months ago

@Janardhanan Sivaramakrishnan I couldn't follow the point you wanted to make.

Okay, I went through your comment again.

So are we dealing with the difference between the words "invalid" and "meaningless"?

Moreover, the question states the full domain of Integers (positive as well as negative). So the inequality is meaningful for the positive numbers and meaningless (not meaningful) for the negative numbers. Why can't I say that it's valid for positive numbers and invalid (not valid) for negative numbers.

I am not so thoroughly acquainted with terminology used in higher maths. But if we cannot say that "invalid" and "meaningless" are same things as per the context of our problem. Then I don't mind asking a moderator to change the word 'valid' with 'meaningful' in the options.

:)

Soumo Mukherjee - 6 years, 4 months ago

Not exactly. It holds true for all integers greater than or equal to 0 .

Shashank Kancherla - 6 years, 4 months ago

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No where in the question did we mention that we are only dealing with integers greater than or equal to 0. Niranjan Khanderia is correct.

Soumo Mukherjee - 6 years, 4 months ago

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I know he is right. I was pointing out that his solution failed to include z=0 earlier. He added that now though .

Shashank Kancherla - 6 years, 4 months ago

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@Shashank Kancherla oops..sorry I overlooked it.. :)

Soumo Mukherjee - 6 years, 4 months ago

Thanks. Technically I was correct. But it would be better if 0 is included. It seems that I had put 1 instead of 0 absentmindedly.

Niranjan Khanderia - 6 years, 4 months ago

i thought the 2 options said same things, i am wrong though.

Mardokay Mosazghi - 6 years, 4 months ago

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I too was puzzled before I understood.

Niranjan Khanderia - 6 years, 4 months ago

Do you mean "not valid for z < 0 "?

Calvin Lin Staff - 6 years, 4 months ago

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I have made correction. Thanks.

Niranjan Khanderia - 6 years, 4 months ago

in the case of (0, 1) and (1, infinity)!

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