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Oct
8
comment Without Lagrange's theorem: If $H$ is a subgroup of odd order of $S_n$, then it is a subgroup of $A_n$.
@MarshalKurosh, a permutation of odd parity applied an odd number of times gives a permutation of odd parity. Since the identity permutation has even parity, it follows that any permutation of odd parity has even order, whence every permutation of odd order is even and a member of $A_n$.
Oct
7
comment Matrix Algebra Question (Linear Algebra)
I think you're missing dfeuer's point. If you equate $A_{1,1}^3$ to $2A_{1,1}$ you get $-4 + 2(2-a) = -4$, which has one solution. Then it's just a case of checking it against the other three cells.
Oct
7
comment Filling 4l, 5l bottles from two 10l bottles
I think there is some ambiguity here as to what the desired outcome is. Does "take 2 litres of water each" imply that the water from the two big bottles shouldn't be mixed? Or is all of the water interchangeable, such that this should be understood only as saying that the big bottles should finish each containing 8 litres?
Oct
7
comment What is the upper bound on the error of a matrix multiplication
What have you tried? Where do you get stuck?
Oct
4
reviewed Approve Show $G$ is isomorphic to the multiplicative group $\mathbb{R}^\times$
Oct
4
comment Logarithms and big O notation
Technically $O$-notation is used for upper bounds without any guarantee of tightness, so you could answer $O(n)$ to both questions.
Oct
3
reviewed Looks OK Is there a completion of Laurent series w.r.t. integration?
Oct
3
reviewed Reviewed Show that $\int_{0}^{\infty}\frac{\cos(at)-\cos(bt)}{t} =\ln\frac{b}{a}$
Oct
3
reviewed Reviewed How can I convert an axis-angle representation to a Euler angle representation
Oct
3
comment How can I convert an axis-angle representation to a Euler angle representation
The key terms I think you're missing are axis-angle and Euler angle representations. There doesn't seem to be an existing question about the conversion from axis-angle to Euler angles, but knowing the terminology is a good starting point when searching.
Oct
3
reviewed Reviewed Riddle: 1 question to know if the number is 1, 2 or 3
Oct
3
comment An Olympiad Problem (tiling a rectangle with the L-tetromino)
What have you tried? Where do your ideas fail?
Oct
3
reviewed Leave Open Area of an irregular polygon
Oct
2
reviewed Close Proving $\sqrt{\tan(\alpha)\tan(\beta)+5}+\sqrt{\tan(\alpha)\tan(\gamma)+5}+\sqrt{\tan(\beta)\tan(\gamma)+5}\le4\sqrt{3}$
Oct
1
reviewed Close If $\{f_i\}$ generate the unit ideal in a ring, so do $\{f_i^N\}$ for any positive $N$
Oct
1
reviewed Close Consider the complex exponential function $f \colon {\mathbb C} \to {\mathbb C}$ given by $f(z) = e^z$.
Oct
1
reviewed Close Computing all simple paths in a distributive lattice in parallel.
Sep
29
reviewed Leave Open Prove $F_{1}^{2}+F_{2}^{2}+\dots+F_{n}^{2}=F_{n}F_{n+1}$
Sep
29
reviewed Reviewed Implicit Differentiation, $\frac{dy}{dx}$, parallel tangent
Sep
28
reviewed Close A Probability problem listed in the excercise of limit theorems (!)