Carlos Eugenio Thompson Pinzón
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 Feb11 comment How do you define the derivative of a function without an argument? @GitGud, I know. My point is that $f'$ is just the function generated by point-wise calculating $f'(x)$ in each point $x$. At least whenever $f$ is derivable in $x$. I might further declare a derivate operator but that does not define the derivative of a function. Feb11 comment How do you define the derivative of a function without an argument? $f':\mathbb R\to\mathbb R$, $x\mapsto f'(x):=\lim_{h\to 0}\frac{f(x+h)-f(x)}{h}$ Feb1 comment what can we say about $f(x)= |\cos x| + |\sin x|$ Note that if 4 is true, then 2 is false. Why?, also check $f(0)$ Feb1 revised what can we say about $f(x)= |\cos x| + |\sin x|$ TeXing a little Dec10 awarded Caucus Dec10 comment Suppose $A,B,C$ are sets. Prove that $A\mathbin\triangle B\subseteq C \iff A\cup C=B\cup C$. @kuhaku I used Inkscape. I'm not sure if this apply as a rigorous proof. The one qualifying the proof should define what is rigorous enough. Nov2 awarded Nice Answer Oct7 awarded Yearling Oct1 comment How to transform the following logical expression into English More like there is an engineer such as for every accountant who manages this engineer,there is a person who the accountant manages. Oct1 revised How to transform the following logical expression into English TeXing a little Oct1 revised Proof about a subset of a metric space TeXing a little Oct1 revised Determine whether {¬q∧(p→q)}→¬p is tautology added 41 characters in body Oct1 revised Find the values of $a$ and $b$ so that f will be continuous on $(-\infty, \infty)$ TeXing a little Oct1 reviewed Approve A logic exercise (finite satisfiability) Sep30 revised Decimal expansion of a Cauchy sequence minor corrections. Sep30 comment Decimal expansion of a Cauchy sequence @ChristianBueno The second $b_n$ sequence is pretty close to the decimal expansion of $a$, although in some cases the $n$th digit might be off by 1. Sep30 awarded Explainer Sep16 revised Recursive definition of multiplication TeXing a little Apr22 awarded Enlightened Apr22 awarded Nice Answer