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Feb
4
revised New proof about normal matrix is diagonalizable.
added 4 characters in body
Feb
4
answered New proof about normal matrix is diagonalizable.
Jan
29
awarded  Yearling
Sep
30
awarded  Explainer
Jul
2
awarded  Curious
May
24
revised Does every function with $f_x,f_y>0,f_{xx},f_{yy}<0$ with particular condition have to satisfy $f_{xy}/f_{xx} = -x/y$?
deleted 3 characters in body
May
24
comment Does every function with $f_x,f_y>0,f_{xx},f_{yy}<0$ with particular condition have to satisfy $f_{xy}/f_{xx} = -x/y$?
When you say $\infty$, it is $+\infty$ or $-\infty$?
May
21
answered Inverse of a sum of positive definite matrices
May
20
answered Proving $A+2B+3C+4D < 2.5$ with given conditions
May
20
comment If $f'(x) = 0$ for all $x \in \mathbb{Q}$, is $f$ constant?
You may want to consider the fundamental theorem of Lebesgue integral calculus, which requires $f'(x)=0$ almost everywhere to get to your result. However, $\mathbb{Q}$ is far away from almost everywhere..
Feb
12
awarded  Nice Answer
Jan
29
awarded  Yearling
Sep
12
accepted Maximal abelian subgroups in a $p$-group are always normal?
Sep
12
comment Maximal abelian subgroups in a $p$-group are always normal?
thanks, I didn't realise it was so simple.
Sep
11
comment Maximal abelian subgroups in a $p$-group are always normal?
@DonAntonio, yeah, I am assuming the $p$-group is finite. But I am talking about maximal among abelian subgroups, not just maximal among any subgroups.
Sep
11
asked Maximal abelian subgroups in a $p$-group are always normal?
Aug
5
comment $ \frac {dy}{dx} \sin y = (1-x\cos y)\cos y$
Hint: $\sin ydy=-d\cos y$.
Jul
22
comment Are these 2 graphs isomorphic?
@MarkMcClure, do you know this kind of animation is available by tex coding or not?
Jul
22
answered Group Theory Normal Subgroups
Jul
21
comment Solving $x^2-7[x]+5=0.$ to find values of $x$.
Hint: find the intersection of $y=x^2+5$ and $y=7[x]$.