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1h
comment Are there numbers such that A + B = 10A+B?
Did you asked which two 2-digit numbers AB and CD sum up to a 4-digit number ABCD in the first title of you question?
1h
comment Solving an equation that contains a logarithm
I was not satisfied with the formulation of the problem. My English is not very good, but I think 'express' is an appropriate term . If it not, please ´help tofind the right word.
1h
comment Resultant Temperature
14*m_1 + 38*m_3 = 28*(m_1 + m_3) means that the resultant temperature is 28C if the temperature of the first liquid was 14C and the third was 38C. The calculation is right but you answered another question.
Jul
1
comment Defining exponentiation on the integers
@Cameron Buie: yes, I forgot them. Thx
Jul
1
comment Defining exponentiation on the integers
of course you could. use the biomial theorem.
Jun
30
comment Logic problem involving sum of digits
@Mike: you are right, but I mentioned that one can construct other solutions by adding/removing zeros
Jun
30
comment Complex numbers $z$ satisfying $|z−a|+|z+a| = 2|b|\Leftrightarrow |a|\le |b|$.
If you draw the complex numbers as points in the plane your equation describes what kind of figure?
Jun
30
comment Complex numbers $z$ satisfying $|z−a|+|z+a| = 2|b|\Leftrightarrow |a|\le |b|$.
What is the first implication and what is the second one? Please show us the prove.
Jun
30
comment Are 7 and 49 coprime?
@Ben: better than "Thanks": accept the answer.
Jun
30
comment Logic problem involving sum of digits
$11101110111^2=123234645696546432321$ is another one
Jun
30
comment Logic problem involving sum of digits
@Donkey Kong: No, $S(n^2)$ means squaring the number $n$ and then taking the sum of digit.
Jan
16
comment Cubes differences and primality
I completed the prove, I hope there are no errors. But I can't see how that will help you to avoid trial an error. Can you explain this?
Jan
16
comment Cubes differences and primality
@Ross Millikan, thank's
Jan
12
comment Is there an intuitive explanation for $ x^2+y^2=7 z^2 $ doesn't have any integer solution?
I still I can't see where you use the fact that $x^2+y^2=z^2$ has infinite integer solutions.
Jan
12
comment Is there an intuitive explanation for $ x^2+y^2=7 z^2 $ doesn't have any integer solution?
That is neither a answer to the question ("Does this fact ...") nor does this give us a complete answer to the more usefull question: what are the integer solutions of the equation.
Jan
10
comment how can I prove that $\frac{\arctan x}{x }< 1$?
@enzolib: thanks, I added this to the answer.
Jan
9
comment How do I find which set of functions is linearly independent?
and how do you prove that all other are not linear dependent?
Jan
5
comment Better way of factorising $x^2-a^2+x+a$
here is a more systematic technic math.stackexchange.com/a/544042/11206 but maybe much more than you want.
Jan
5
comment Better way of factorising $x^2-a^2+x+a$
+1, but maybe incomprehensibly to the OP
Jan
5
comment Better way of factorising $x^2-a^2+x+a$
$x({1^2}+1)-a(1^2-1)$ equals $2x$ and not ${x^2}-{a^2}+x+a$. As Hurkyl already noted, your attempt to create a common factor contains an error.