• The circle of Apollonius

    By definition, a circle is the locus of all points equidistant from a fixed center. However, the circle of Apollonius is defined differently. In the following post I will define and construct an Apollonian circle.
  • Asymptotic Differentiable Function

    Let $f$ be any function asymptotic at zero. Prove/Disprove:
    If $f$ is differentiable everywhere in its domain, then $\lim_{x\to \infty}f\;'(x)$ must be equal to zero?
  • Finding which package provides a command

    Suppose a command is not available in the system and we need to install it. How do we find a suitable package that provide this command? In Debian or Ubuntu we can simply run the following command
  • Steinhaus theorem

    Let $\lambda$ be Borel measure.
    1. If $A$ is mesuarable and $\lambda(A)>0$, then $A-A=\left\{ x-y\; :\; x,y\in A \right\}$ contains a segment $I$ such that $0\in I$
    2. If $A, B$ are measurable sets and $\lambda(A), \lambda(B)>0$, then $A+B$ contains a segment I.
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