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comment Why is there two versions of the rotation matrix?
There is the additional complication that one can define active and passive transformations (which is always confusing for people).
Oct
11
revised Efficient software implementation of $x^2+3y^2=N$
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Oct
11
revised Efficient software implementation of $x^2+3y^2=N$
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Oct
11
answered Efficient software implementation of $x^2+3y^2=N$
Sep
30
awarded  Explainer
Sep
10
answered When is a point in the plane inside a simple closed path?
Sep
1
comment Can I solve an Euler differential equation by using the Frobenius method?
You have to set that $n \geq 0$, i.e., $a_{n<0}=0$ and $a_0 \neq 0$, otherwise $\sigma$ is not well defined. Take then a look at the equation for $n=0$.
Aug
27
comment Prove that there exists no smallest positive real number
From the inequality $x/2 \geq x$ you get directly a contradiction when dividing by $x$.
Aug
23
comment If the product $fg$ is Riemann integrable then are $f$ and $g$ individually integrable?
I like this one !
Aug
22
comment Shorter way to integrate $\int \frac{x^9}{(x^2+4)^6} \, \mathrm{d}x$
You seem to be given answers: In this case it is usually easier to take derivatives of all the answers to check whether they match the integrand.
Aug
22
revised Shorter way to integrate $\int \frac{x^9}{(x^2+4)^6} \, \mathrm{d}x$
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Aug
22
answered Shorter way to integrate $\int \frac{x^9}{(x^2+4)^6} \, \mathrm{d}x$
Aug
21
comment Integral of inverse of square root of a quadratic
Do you want the electric field in the center of the tube?
Aug
21
comment Integral of inverse of square root of a quadratic
What is the question?
Aug
19
comment Find the 1005th digit after the decimal point expansion of the square root of N.
Do you know what the first digits (the ones before the decimal point and the 1004 first digits after it) look like?
Aug
14
comment A Poisson process question
Do you have a link to the old post?
Aug
14
answered Can multidimensional eigenfunction problems be solved to arbitrary precision in constant memory usage?
Aug
14
answered Eigenvalues and eigenvectors of a non-symmetric matrix which is a product of 2 symmetric matrices?
Aug
14
comment Eigenvalues and eigenvectors of a non-symmetric matrix which is a product of 2 symmetric matrices?
Why do you think that this problem has a simple solution?
Aug
12
comment solve $\cos y \sin(2x) dx + (\cos^2y - \cos^2x)dy = 0$
@GaneshTadi: yes, now divide by $\sin(2x)$. The resulting equation only involves $y$. In the end $f(y)$ can be solved, e.g., by separation.