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The question is this:

Question: Identify a suitable universe of discourse such that the predicate z2 + 4 = 0 has existential import.

Now if you try to factor this equation, you will see that it is not possible.

If you try to solve for z, what you get is this:

z2 - 4i2

(z + 2i) (z - 2i)

z = +-2i

So The only suitable universe of discourse is complex numbers.

Is my answer correct?

Edit: In set theory notation, it would look something like this ᗄx∈ in the complex number set. Please also check that my notation is correct.

Deathslice
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  • This wasn't a set theory question before, and it's not a set theory question now. – Asaf Karagila Jun 16 '15 at 19:32
  • "A" suitable universe of discourse is the complex numbers. It is far from the only such universe. Also, you made several mistakes in solving for $z$; check your computations and recall the definition of square root. – guest Jun 16 '15 at 20:23
  • Yes I will edit my mistake. – Deathslice Jun 16 '15 at 21:06
  • @guest Alright I have fixed my mistakes. I can't believe I didn't notice them. Probably because I was typing too fast and didn't proofread what I was typing. – Deathslice Jun 16 '15 at 21:10
  • @AsafKaragila Yes your're correct but the next question asked for me to put it in the format that you see in the edit section. That is why I also is asked if that was correct as well. – Deathslice Jun 16 '15 at 21:14

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