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  1. Why is $1/i$ equal to $-i$? - Mathematics Stack Exchange

    May 11, 2015 · 11 There are multiple ways of writing out a given complex number, or a number in general. Usually we reduce things to the "simplest" terms for display -- saying $0$ is a lot …

  2. abstract algebra - Prove that 1+1=2 - Mathematics Stack Exchange

    Jan 15, 2013 · Possible Duplicate: How do I convince someone that $1+1=2$ may not necessarily be true? I once read that some mathematicians provided a very length proof of $1+1=2$. Can …

  3. Formal proof for $ (-1) \times (-1) = 1$ - Mathematics Stack …

    Jun 13, 2020 · Is there a formal proof for $(-1) \\times (-1) = 1$? It's a fundamental formula not only in arithmetic but also in the whole of math. Is there a proof for it or is it just assumed?

  4. What is the value of $1^i$? - Mathematics Stack Exchange

    Aug 30, 2010 · There are infinitely many possible values for $1^i$, corresponding to different branches of the complex logarithm. The confusing point here is that the formula $1^x = 1$ is …

  5. Why is $1$ not a prime number? - Mathematics Stack Exchange

    Jun 28, 2022 · 49 actually 1 was considered a prime number until the beginning of 20th century. Unique factorization was a driving force beneath its changing of status, since it's formulation is …

  6. factorial - Why does 0! = 1? - Mathematics Stack Exchange

    Intending on marking as accepted, because I'm no mathematician and this response makes sense to a commoner. However, I'm still curious why there is 1 way to permute 0 things, …

  7. If $A A^{-1} = I$, does that automatically imply $A^{-1} A = I$?

    Mar 30, 2020 · This is same as AA -1. It means that we first apply the A -1 transformation which will take as to some plane having different basis vectors. If we think what is the inverse of A -1 …

  8. algebra precalculus - Prove $0! = 1$ from first principles ...

    Feb 8, 2011 · How can I prove from first principles that $0!$ is equal to $1$?

  9. General term formula of series 1/1 + 1/2 + 1/3 ... +1/n

    This sum is called $H_n$ the $n$th"harmonic number" and has no known closed form.

  10. power series - How can we know the answer to 1-1+1-1+1 ...

    The series does not converge, because as you observe, the partial sums $1,0,1,0,\ldots$ oscillate and do not approach a single limit. There are various ways to assign values to some divergent …