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Nov
21
comment Using Vieta's Formulas to find expression involving polynomial roots
$1/a_1+1/a_2+1/a_3=(a_2 a_3 +a_1 a_3+a_1 a_2)/(a_1 a_2 a_3)$ and en.wikipedia.org/wiki/Vieta%27s_formulas
Nov
11
revised A basis $B$ is orthonormal if and only if $\langle f,g \rangle=[f]_B\cdot [g]_B$ for all $f$ and $g$ in $V$
added 47 characters in body; edited title
Nov
6
revised Determine for which constants $a$, $b$, $c$ and $d$ it is true that $f \circ g = g \circ f$.
added 16 characters in body; edited title
Nov
4
comment Is $\gamma(t)=\cos^2(t)$ a characteristic function?
$\cos^2 t = \dfrac{1+\cos 2t}{2}=\dfrac{1}{2}e^{0}+...$ and $\cos x= \dfrac{e^{ix}+e^{-ix}}{2}$
Nov
4
revised $\sum x_{k}=1$ then, what is the maximal value of $\sum x_{k}^{2}\sum kx_{k} $
edited tags
Nov
4
comment Very elementary question concerning open intervals and their intersection
What means (ca) tag? I suppose you wanted (calculus) or?
Nov
4
revised If $\sum f_n$ is absolutely convergent and uniformly convergent $\Longrightarrow$ $\sum \|f_n\|$ is uniformly convergent.
added 7 characters in body; edited tags; edited title
Oct
29
reviewed Approve suggested edit on Vector subspace of polynomials
Oct
28
reviewed Approve suggested edit on Is the first partial derivative of the cumulative joint density function equal to the marginal density
Oct
22
comment Prove that $\sup(A-B) = \sup(A) - \inf(B)$
I think that we need that sets $X$ and $Y$ are bounded in some way for first hint.
Sep
30
awarded  Explainer
Sep
22
accepted Show that exists a finite subset in $\mathcal{L}$-theory
Sep
6
comment Show that exists a finite subset in $\mathcal{L}$-theory
I have some doubts. Please see my comment bellow my question in comments.
Sep
6
comment Show that exists a finite subset in $\mathcal{L}$-theory
@MauroALLEGRANZA See please my comment above.
Sep
6
comment Show that exists a finite subset in $\mathcal{L}$-theory
@tomasz Is YonedaLenna right? Because choosing $\sigma$ depends on $\mathcal{M}$, so do we really have $T \models \sigma$? I am confused now.
Sep
5
asked Show that exists a finite subset in $\mathcal{L}$-theory
Aug
16
comment Definite integral $\int_{-64}^{1}\frac{dx}{x^{1/3}}$
@ClaudeLeibovici I agree with you. This is Cauchy principal value.
Jul
22
reviewed Approve suggested edit on Find the volume of the solid enclosed by the paraboloids
Jul
19
comment The Dirac Delta Distribution $\delta_0 : D \to \mathbb R$ is not regular
You can see here also some ideas.
Jul
17
reviewed Approve suggested edit on Actuary P/1 Exam Question