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Fabrizio G's user avatar
Fabrizio G's user avatar
Fabrizio G's user avatar
Fabrizio G
  • Member for 5 years, 3 months
  • Last seen this week
  • Argentina
9 votes
2 answers
126 views

Find the sum $\sum\limits_{k=0}^\infty (-2)^k\frac{k+2}{k+1}x^k$

8 votes
1 answer
4k views

Is the product $AB$ invertible if $A$ is invertible and $B$ is non-invertible?

5 votes
1 answer
165 views

Minimum cost of a connected graph

5 votes
2 answers
101 views

Negation of a statement with an inequality.

4 votes
0 answers
83 views

There is no injective continuous map from $(\mathbb{R}-\mathbb{Q})\times\mathbb{R}$ to $\mathbb{R}$.

4 votes
1 answer
670 views

Find the extreme values of $x^2+xy+y^2-27=0$

3 votes
2 answers
168 views

If $\int_a^\infty f(x)dx$ exists (converges), then $\int_a^\infty \frac{f(x)}{x}dx$ exists

3 votes
1 answer
98 views

Characterize open sets of this quotient topology.

3 votes
1 answer
197 views

Isomorphism between two vector spaces.

3 votes
0 answers
19 views

Real eigenspaces of a matrix $A\in\mathcal{M}_{2\times 2}(\mathbb{R})$ are the union of straight lines trajectories and the fixed point $y\equiv 0$

3 votes
1 answer
104 views

In a group, if $g^{-1}h\in S(x)$ (stabilizer), then $gS(x)=hS(x)$ (as left cosets).

3 votes
0 answers
71 views

If $R$ is a ring without divisors of $0$ (not necessarily commutative), is it true that for every $x\neq 0$, $xR=Rx$?

3 votes
0 answers
44 views

Stability of a $3\times 3$ system of non-linear differential equations.

2 votes
0 answers
28 views

Gaussian curvature of Hyperbolic Plane.

2 votes
0 answers
16 views

Matching number of a graph is equal to the independence number of its line graph.

2 votes
1 answer
40 views

If a graph is 1-factoreable, then it has no cut vertex.

2 votes
1 answer
80 views

Let $\sigma\in S_n$. Then, $\sigma x=x\iff$ the only orbit of $x$ by certain group action is trivial.

2 votes
1 answer
87 views

Tietze Extension Theorem - Munkres Section 35, Theorem 35.1

2 votes
2 answers
340 views

Check if two functions are linearly independent.

2 votes
1 answer
117 views

Euler cycle in a $m\times n$ rectangular grid.

2 votes
0 answers
62 views

Show that if all orthogonal trajectories to a curve pass through the same point $P_0$, then the curve is a circle.

2 votes
1 answer
185 views

Homogeneous linear differential equation $y'+a(x)y=0$ where $a$ is continuous and periodic.

2 votes
0 answers
68 views

Find a counterexample for this ODE.

2 votes
1 answer
156 views

Is it possible that $\liminf=+\infty$?

2 votes
1 answer
63 views

Show two curves have constant lifting.

2 votes
1 answer
859 views

Smallest value for the number of edges in a non-planar graph?

2 votes
4 answers
675 views

Does the series $\sum \frac{1}{\ln^3(k)}$ converge or diverge?

2 votes
1 answer
70 views

Show $g:X^2\to \mathbb{R}$ is a metric. [duplicate]

2 votes
2 answers
40 views

Find a family $\mathscr{F}$ such that $\mathscr{F}\subset \mathcal{M}\subset{\Phi_\mathscr{F}}$ with proper subsets.

2 votes
1 answer
64 views

Show that inclusion function $i:\mathbb{R}^\omega\to\mathbb{R}^\infty$ is continuous but not an homemorphism in its image.