Emanuele Paolini
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 Sep 29 answered Using a function to order an integer's digits from least to greatest? Sep 29 comment Using a function to order an integer's digits from least to greatest? The function you describe is perfectly mathematical. Probably what you mean is if one can write such a function as a composition of "elementary" function (where elementary functions are the ones you see on a pocket calculator). In this sense the answer is probably not. Sep 29 comment Counting numbers in a sequence - explain “Add 1 before you're done” rule @psmears: ops :-D I removed my comment Sep 28 comment Proving that the complex function $z^n$ is continuous I think it is easier to prove that the product of continuous functions is continuous. The result then follows by induction. Sep 27 comment Solving limits without using L'Hôpital's rule Taylor at order 1 is simply the definition of derivative. L'Hospital theorem is much more than that... Sep 26 revised What condition should an $m\times n$ matrix $A$ meet for $x\mapsto\|Ax\|$ to define a vector norm added 13 characters in body Sep 26 comment What condition should an $m\times n$ matrix $A$ meet for $x\mapsto\|Ax\|$ to define a vector norm right, corrected! Sep 26 answered What condition should an $m\times n$ matrix $A$ meet for $x\mapsto\|Ax\|$ to define a vector norm Sep 26 comment Show that $x\mapsto e^x$ is continuous. Sep 26 comment Is -2 is a root of the equation : $\sqrt {x^2 - 8} = \sqrt {3x + 2}$? you are saying that sqrt(-4) = 2i. This is questionable, I have never seen such a definition. Sep 26 comment Is -2 is a root of the equation : $\sqrt {x^2 - 8} = \sqrt {3x + 2}$? Anyway the square root is not defined. Sep 26 answered Set question, relations, equivalence classes Sep 26 revised Set question, relations, equivalence classes deleted 1 character in body Sep 26 answered Is -2 is a root of the equation : $\sqrt {x^2 - 8} = \sqrt {3x + 2}$? Sep 26 revised Is -2 is a root of the equation : $\sqrt {x^2 - 8} = \sqrt {3x + 2}$? deleted 12 characters in body Sep 25 revised Show that $x\mapsto e^x$ is continuous. added 26 characters in body Sep 25 revised Show that $x\mapsto e^x$ is continuous. added 59 characters in body Sep 25 comment Show that $x\mapsto e^x$ is continuous. right... I add it! Sep 25 revised Solve the following equation. Check all proposed solutions. edited tags Sep 25 comment Can you fit every single permutation of a triangle inside a circle with all three points touching the edges of the circle The statement is not clear. What are the permutations of a triangle? The circle is fixed?