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André Nicolas

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122
Why can ALL quadratic equations be solved by the quadratic formula?
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96
Is the following matrix invertible?
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56
“Negative” versus “Minus”
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49
Does multiplying polynomials ever decrease the number of terms?
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49
Why don't we define “imaginary” numbers for every “impossibility”?
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45
Root Calculation by Hand
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41
How to convince a layman that the $\pi = 4$ proof is wrong?
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37
What is the chance to get a parking ticket in half an hour if the chance to get a ticket is 80% in 1 hour?
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34
are all $n!$ ($n>3$) the difference of two squares?
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33
Show that $A_n=\sum\limits_{k=1}^n \sin k $ is bounded?
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33
Why ${ \sum\limits_{n=1}^{\infty} \frac{1}{n} }$ is divergent , but ${ \sum\limits_{n=1}^{\infty} \frac{1}{n^2} }$ is convergent?
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32
Find the limit $\lim \limits_{n\to \infty }\cos \left(\pi\sqrt{n^{2}-n} \right)$
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29
Does iterating $n \to 2n+1$ always eventually produce a prime number?
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29
Do all natural numbers have a nonzero multiple that is a palindrome in base 10?
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28
How I can prove that converges to 2?
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25
A simple way to evaluate $\int_{-a}^a \frac{x^2}{x^4+1} \, \mathrm dx$?
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25
If you have a $1$ in $36$ chance of winning an event. What is the probability that you will win at least once in $36$ tries?
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24
how to prove 437 divides 18!+1?
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23
Gödel's incompleteness theorem and real closed fields
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23
Can $x^{n}-1$ be prime if $x$ is not a power of $2$ and $n$ is odd?
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23
For what values of $n$ is $n^2+n+2$ a power of $2$?
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22
Can you raise a number to an irrational exponent?
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22
$\sum a_n$ converges absolutely, does $\sum (a_n + \cdots + a_n^n)$ converge
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22
How to integrate $\int\frac{1}{1+\cos{x}}\ dx$?
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21
Is a dense subset of the plane always dense in some line segment?
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21
Irrationality of “primes coded in binary”
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21
Showing that $\frac{\sqrt[n]{n!}}{n}$ $\rightarrow \frac{1}{e}$
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20
Uncountable closed set of irrational numbers
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19
How can I find $\int\frac1{\sqrt[4]{1+x^4}}\mathrm dx$?
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19
The so-called rule of 72 (or rather, 69)
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