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5h
comment Solving ODE $x' = \lambda x^2$
You are missing the trivial solution $x=0$.
5h
comment Solving ODE $x' = \lambda x^2$
What is your solution?
5h
comment Simple inequality proof in analysis
Yes, you must prove that is it always false if $a>b$.
5h
comment Simple inequality proof in analysis
No. You just proved that $1>0$, which is rather clear... You tried to prove a theorem by showing that it is indeed correct in a single case, and this is not enough.
5h
comment Questions about Bolzano-Weierstrass Theorem
Unclear what you are asking. Why should Lang's proof be odd? What can't you understand?
6h
comment Simple inequality proof in analysis
Because you are not allowed to reduce to a numerical case like $a=1$ and $b=0$. You should produce a proof that works with any admissible choice of the parameters. In other words, you proved only a particular case, but the general case is still open.
6h
answered Simple inequality proof in analysis
Jan
26
comment Show that elements $u \in W^{1,\infty}(U)$ have continuous representatives
I believe that your functions have a bounded derivative, so that they have Lipschitz representatives...
Jan
26
comment The set of differentiable functions such that $f'(2)=b$ is a linear subspace if and only if $b=0$??
You simply cannot enumerate all the points of $(0,3)$. The set of all sequences is totally useless here.
Jan
26
comment The set of differentiable functions such that $f'(2)=b$ is a linear subspace if and only if $b=0$??
$\Gamma \subset \mathbb{R}^2$. Sorry, can you write down your definition of $\mathbb{R}^\infty$?
Jan
26
comment The set of differentiable functions such that $f'(2)=b$ is a linear subspace if and only if $b=0$??
You are just identifying $f$ with its graph: $\Gamma = \{(x,f(x)) \mid x \in (0,3)\}$...
Jan
26
revised Suppose $f(x,y)=c(x^{m}+y^{n})-dx^{a}y^{b}+sin(x+y^{2})$, show that f is greater than
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Jan
26
comment Derivative of bilinear forms
$\mathbb{R}^n \times \mathbb{R}^n \sim \mathbb{R}^{n^2}$.
Jan
26
answered The set of differentiable functions such that $f'(2)=b$ is a linear subspace if and only if $b=0$??
Jan
26
comment If $\lim\limits_{z\to z_0} f(z)=0$ and $|g(z)|<M$, for all $z$, with $M$ being a positive number, then we have $\lim\limits_{z\to z_0} f(z)g(z)=0$.
After choosing $\delta>0$, you are done.
Jan
26
comment Diagonalization of a quadratic form with parameter $k \in \mathbb{R}$: $q(x,y,z)=(2+k)x^2+2y^2+kz^2+4xy-2kxz$
Viceversa is better: you show us your approach.
Jan
26
comment If $\lim\limits_{z\to z_0} f(z)=0$ and $|g(z)|<M$, for all $z$, with $M$ being a positive number, then we have $\lim\limits_{z\to z_0} f(z)g(z)=0$.
Your assumptions are unclear. However, if the upper bound $|g(\cdot)| \leq M$ holds everywhere, then $\delta_2$ is useless to conclude.
Jan
26
answered Matrix notation of vectors?
Jan
26
revised evaluating an indefinite and improper integral
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Jan
26
comment Counterexample Poincaré Inequality for $H_0^1$ in 2D
Possible related question: mathoverflow.net/questions/39141/…