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Aug
24
revised Geometric sequence problem
latex
Aug
20
answered Interesting and unexpected applications of $\pi$
Aug
16
comment $u=xf(xy)$, show that $xu_{xx}-yu_{xy} = 0$
So please post the solution as an answer
Aug
16
comment $u=xf(xy)$, show that $xu_{xx}-yu_{xy} = 0$
There is no $f_{xx}$ or $f_{xy}$ but only an $f'$ or $f''$
Aug
16
comment $u=xf(xy)$, show that $xu_{xx}-yu_{xy} = 0$
your calculation of $u_x$ is wrong. Choose $u(x,y)=f(xy)=c$ then you get $u_x=c$ and that is wrong.
Aug
16
revised If $3x^2 -2x+7=0$ then $(x-\frac{1}{3})^2 =$?
format, typos wording
Aug
4
comment Difference between ${2\over 9}$ and ${22\over 99}$?
calculate their difference!
Aug
3
comment Prove that the Mandelbrot Set Is A Closed Set
the intersection of closed sets is closed.
Jul
31
reviewed Reject Second differential of the norm in an infinite dimensional Hilbert space
Jul
27
comment Weird Induction…?
your second formula is apparerently wong: it says that $\binom{n + k + 1}{k}$ is constant, independent of $k$. So check your formula, you made an error. It is $$\sum_{i = 0}^{k} \binom{n + i}{i} = \binom{n + k + 1}{k}$$ for $0 \leq k \leq n$
Jul
16
revised Calculate 2000! (mod 2003)
latex, mod
Jul
16
comment Calculate 2000! (mod 2003)
Of course you have to prove that 2003 is a prime otherwise you can't be sure that the result is true.
Jul
16
reviewed Approve Counting chain maps
Jul
13
revised Solving the Logarithmic equation $\log_x (3-2\sqrt2)=2$
latex, title
Jul
12
reviewed Approve Cauchy-Schwarz inequality proof (but not the usual one)
Jul
10
reviewed Approve $R^2\setminus K, K$ compact, is not simply connected
Jul
10
revised $R^2\setminus K, K$ compact, is not simply connected
latex symbol
Jul
10
revised Exercise 1 on page 10 in Naive Set Theory, following Axiom of Pairing
some missing formulas added
Jul
10
revised Exercise 1 on page 10 in Naive Set Theory, following Axiom of Pairing
typo
Jul
10
revised Exercise 1 on page 10 in Naive Set Theory, following Axiom of Pairing
added 171 characters in body