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Nov
6
answered Prove that if $3\mid n^2 $ then $3\mid n $.
Nov
6
comment Prove that if $3\mid n^2 $ then $3\mid n $.
what's your definition of prime number?
Nov
6
comment If $f$ is bounded and twice differentiable in $\mathbb{R}$, show that there exists $\xi\in\mathbb{R}$, s.t. $f''(\xi)=0$.
Lemma 3 is false: take $f(x)=atan(x)$
Nov
6
comment If $f$ is bounded and twice differentiable in $\mathbb{R}$, show that there exists $\xi\in\mathbb{R}$, s.t. $f''(\xi)=0$.
en.wikipedia.org/wiki/Darboux%27s_theorem_%28analysis%29
Nov
6
comment If $f$ is bounded and twice differentiable in $\mathbb{R}$, show that there exists $\xi\in\mathbb{R}$, s.t. $f''(\xi)=0$.
The intermediate value theorem is true for the derivative of a function even if the derivative is not continuous.
Nov
6
revised If $f$ is bounded and twice differentiable in $\mathbb{R}$, show that there exists $\xi\in\mathbb{R}$, s.t. $f''(\xi)=0$.
added 40 characters in body
Nov
6
answered If $f$ is bounded and twice differentiable in $\mathbb{R}$, show that there exists $\xi\in\mathbb{R}$, s.t. $f''(\xi)=0$.
Nov
4
revised Why is $e^{-f(z)} = 1-z$, when $f(z)=\sum_{n=1}^\infty \frac{z^n}{n}$?
edited body; edited title
Nov
4
asked Pull back of a vector representing a 2-form in $\mathbb R^3$
Oct
30
answered Partitions of $[0,1]$
Oct
28
comment Replace a sum with an integral $\sum\rightarrow \int$
What does the arrow mean?
Oct
28
answered Find the minimum distance between the curves $y^2-xy-2x^2 =0$ and $y^2=x-2$
Oct
28
awarded  geometry
Oct
27
revised Intuition behind a certain limit.
added 188 characters in body
Oct
27
answered Intuition behind a certain limit.
Oct
27
revised Show $(a_n)_{n=m}^{\infty}$ converges to $c$ iff $(a_n)_{n=m'}^{\infty}$ does.
missing part of statement
Oct
27
answered Show $(a_n)_{n=m}^{\infty}$ converges to $c$ iff $(a_n)_{n=m'}^{\infty}$ does.
Oct
27
comment Prove no member of $S = \left\{x \mid x \in \mathbb{Q^+}, x^2 < 2 \right\}$ can be an upper bound for $S$
Suppose that $r\in S$ is an upper bound. You have proven that there exists $r'>r$, $r'\in S$. So $r$ is not an upper bound.
Oct
27
answered Finding maximum area of rectangle with constraint
Oct
27
comment Finding maximum area of rectangle with constraint
$x$ and $y$ are length and width.