914 reputation
17
bio website
location
age
visits member for 8 months
seen 59 mins ago

58m
comment About derivative function
Uh?${}{}{}{}{}$
1d
comment Let A, B and C be sets. Show that $\overline A \cap B \cap C \subseteq (A \cup B)\cap(A \cup C)$
Use that if $x\in X$, then $x\in X\cup Y$ for any set $Y$.
Sep
18
comment What is the identity matrix in N dimensional space?
What does $[2,3,3]$ mean?
Sep
15
comment Isomorphism and Cardinality
How is the operation $\ast$ defined on $G$?
Sep
14
comment Exist a function composed by simple continuous functions that $f:\Bbb R \rightarrow \Bbb N$?
Anaylitic functions are continuous, so any analytic function $f:\Bbb R\to \Bbb N$ must be constant.
Sep
14
comment Exist a function composed by simple continuous functions that $f:\Bbb R \rightarrow \Bbb N$?
What do you mean by analytic?
Sep
13
comment Given S, prove that C is an open cover, but there is no finite subcover of C that covers S.
You can learn how to do it here
Sep
6
comment Basic question on exactness of commutative diagrams.
$j:H\to G$ is defined by $j(h)=h$ for all $h\in H$. The image of $j$, $j(H)$, is $H$.
Aug
31
comment Subgroups and cyclic groups
Take any $g\in G$ different from the identity element. What is $\langle g\rangle$?
Aug
31
comment Judge the convergence of $\sum_{n=0}^\infty 1/\sqrt{n}$
$\dfrac{1}{n}\le\dfrac{1}{\sqrt{n}}$
Aug
31
comment Prove The following geometrically
mathoverflow.net/a/24828
Aug
30
comment Permutation matrices
Have you tried to do this for, say, a small $3\times 3$ matrix $A$ and a permutation matrix $M$?
Aug
19
comment Is division allowed in rings and fields?
You can also see here Division ring
Aug
5
comment Linear Algebra-Intersections and Distances in R3 and R2.
What are your answers?
Aug
5
comment Solve for $x$ in the equation
Hint: Your equation is equivalent to $\dfrac{5^x}{3^x}=2$.
Aug
5
comment What does “single set” mean in this context?
You have a set $X$. You call it $X_1$ if you consider it with the topology $\tau_1$, and $X_2$ with $\tau_2$.
Aug
5
comment Integrating $\frac 1 {\sqrt{x^2 - a^2}}$
Let $x=a\sec(t)$.
Jul
29
comment How do mathematicians know what is known?
math.stackexchange.com/questions/40811/…
Jul
27
comment $f$ is twice differentiable, $f + 2 f^{'} + f^{''} \geq 0$ , prove the following
@Nishant everywhere... where? The domain of $f$ is $[0,1]$.
Jul
12
comment Munkres Topology Exercise 2.q
Yeah, that is true. You're welcome. :)