meta user
network profile
| bio | website | |
|---|---|---|
| location | Besancon, France | |
| age | 33 | |
| visits | member for | 7 months |
| seen | 15 hours ago | |
| stats | profile views | 189 |
|
May 18 |
comment |
What is a perimeter of a sector? @Jawad. Because the sector has also two sides equal to radius. |
|
May 18 |
comment |
What is a perimeter of a sector? @Jawad. Just a question of convention (in the same vein: for area of a cylinder, do you count the two disks?), but it appears the usual convention is counting the radius (see here for example). Anyway it would be useless to have another name for arc length. |
|
May 14 |
comment |
Trigonometry Addition Thereom With Only one exact value? Given that $150=180-30$, it should be easy. |
|
May 14 |
comment |
Solve a cubic polynomial (given one root is four times a second root)? I already answered this. Use the first two equations of Hagen to get a trinomial. |
|
May 14 |
comment |
Integral of $\int^1_0 \frac{dx}{1+e^{2x}}$ Then expand in partial fraction, and it's ok. |
|
May 14 |
comment |
Solve a cubic polynomial (given one root is four times a second root)? And where do you think Vieta's formulas come from? |
|
May 14 |
comment |
Solve a cubic polynomial (given one root is four times a second root)? Just expand $10(x-a)(x-4a)(x-b)$ and say it's equal to $10x^3+23x^2+5x-2$. Then isolate $b$ from the first equation given by Hagen, put it in the second, and you have an equation of degree 2 to solve. |
|
May 12 |
comment |
prove that the unit circle $x^2+y^2=1$ is a closed set @Jyrki, no, Brian Scott is right, it's all about rotating the origin to eliminate the case where angles jump from $0$ to $2\pi$. Of course it's not very difficult to overcome, though a bit tricky. |
|
May 12 |
comment |
prove that the unit circle $x^2+y^2=1$ is a closed set It's ok, except for sequences oscillating around 0: there may be values near $0$ and values near $2\pi$, thus the sequence $\theta_n$ is not convergent. |
|
May 12 |
comment |
Classify the abelian groups of order 81, 144 and 216 For references in english, I think Lang or Dummit & Foote would have this, and much more. |
|
May 12 |
comment |
Line equation - parametric and canonical Ah, ok. You find this by isolating $t$ from the parametric equations. |
|
May 11 |
comment |
How to find prime numbers For formulas (bad approach, but funny), have a look at this and that. @rondo9, there is a formula for next prime number, but probably not what you would expect. |
|
May 10 |
comment |
$\pi$ from the unit circle, $\sqrt 2$ from the unit square but what about $e$? @Inceptio. If you don't understand area, it's liquely you won't understand $pi$ and $\sqrt{2}$ either. |
|
May 10 |
comment |
How to find prime numbers There are actually formulas, but they are all equivalent to some searching algorithm. |
|
May 10 |
comment |
Solve a cubic polynomial? Then the simplest who be to develop $5(x-a)^2(x-b)$ and identify coefficients. |
|
May 10 |
comment |
Solve a cubic polynomial? Hint: if two roots are equal to $a$, then the derivative of your polynomial has $a$ as a root. To see why, just write $P=(x-a)^2 Q$ and differentiate. Hence, you have only an equation of degree 2 to solve. |
|
Apr 15 |
comment |
Prove the inequality $4S \sqrt{3}\le a^2+b^2+c^2$ +1, very nice proof |
|
Apr 15 |
comment |
Coefficient of Taylor Series of $\sqrt{1+x}$ What is the coefficient of $x^n$ in the Taylor series? Hint: there is $f^{(n)}(a)$ in factor. Now, can you differentiate $\sqrt{1+x}$ three times? |
|
Apr 13 |
comment |
Why the SVD is named so… @S.P I know, but it's to be found in history of mathematics. |
|
Apr 13 |
comment |
Why the SVD is named so… en.wikipedia.org/wiki/Singular_value_decomposition#History |
