Are there positive integers $a, b, c$ greater than $2011$ such that: $(a+ \sqrt{b})^c=...2010,2011...$?
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Tags: limit, number theory unsolved, number theory
09.04.2011 10:32
Me no comprehende.
09.04.2011 12:36
RaleD wrote: Are there positive integers $a, b, c$ greater than $2011$ such that: $(a+ \sqrt{b})^c=...2010,2011...$? Yes. For example, $a=7010$, $b=25002012$, $c=1$.
09.04.2011 12:57
nnosipov wrote: RaleD wrote: Are there positive integers $a, b, c$ greater than $2011$ such that: $(a+ \sqrt{b})^c=...2010,2011...$? Yes. For example, $a=7010$, $b=25002012$, $c=1$. OP asked for $c>2011$ too
09.04.2011 14:01
What does it mean by $\left(a+\sqrt{b}\right)^c = \ldots2010,2011\ldots$? Is it the German decimal notation, and thus, are we to find $a$, $b$, and $c$ for which $\left(a+\sqrt{b}\right)^c = \ldots2010.2011\ldots$?
09.04.2011 14:15
Batominovski wrote: What does it mean by $\left(a+\sqrt{b}\right)^c = \ldots2010,2011\ldots$? Is it the German decimal notation, and thus, are we to find $a$, $b$, and $c$ for which $\left(a+\sqrt{b}\right)^c = \ldots2010.2011\ldots$? Yes.
12.04.2011 11:51
Batominovski wrote: What does it mean by $\left(a+\sqrt{b}\right)^c = \ldots2010,2011\ldots$? Is it the German decimal notation, and thus, are we to find $a$, $b$, and $c$ for which $\left(a+\sqrt{b}\right)^c = \ldots2010.2011\ldots$? What is german decimal notation?
12.04.2011 12:26
RaleD wrote: Are there positive integers $a, b, c$ greater than $2011$ such that: $(a+ \sqrt{b})^c=...2010,2011...$? this is very confusing. What is this? $2010.2011$ or else?If it is German notation as the previous post says,then what is the definition of this notation?
12.04.2011 13:21
myro111 wrote: Batominovski wrote: What does it mean by $\left(a+\sqrt{b}\right)^c = \ldots2010,2011\ldots$? Is it the German decimal notation, and thus, are we to find $a$, $b$, and $c$ for which $\left(a+\sqrt{b}\right)^c = \ldots2010.2011\ldots$? What is german decimal notation? Simple, "$12,45$" in Germany is $12.45$ in most other countries. I guess the OP wanted $a$, $b$, and $c$ such that $\left(a+\sqrt{b}\right)^c$ contains $2010.2011$ in its decimal presentation. (It may be, for instance, $7642010.201178643513$.)
12.04.2011 20:44
Problem asks to find $a$, $b$, $c$ (bigger than 2011) such that integer part of $(a+\sqrt{b})^{c}$ is congruent 2010 mod 10000; and it's fractional part is bigger than 0,2011 and smaller than 0,2012. "$,$" is (of course) decimal comma...
20.04.2011 22:14
Stop arguing about notations guys. It's spam Choose $a = 100000000$, $b = 9999999800000000$, and $c = 1797184159$. Obviosly, all three are more than 2011 Hint: $b = (a-1)^2-1$
20.04.2011 22:48
mymath7 wrote: Stop arguing about notations guys. It's spam Choose $a = 100000000$, $b = 9999999800000000$, and $c = 1797184159$. Obviosly, all three are more than 2011 Hint: $b = (a-1)^2-1$ How did you calculate it? Did you do it without a calculator?
21.04.2011 02:28
tom_damrong wrote: How did you calculate it? Did you do it without a calculator? Of course!
21.04.2011 13:57
mymath7 wrote: Obviosly, all three are more than 2011 Actually, the question wasn't to just find three numbers that are greater than 2011 So, can you show that your numbers satisfy given equation?
06.06.2011 15:00
Let $S = {\left( {a + \sqrt b } \right)^c} + {\left( {a - \sqrt b } \right)^c}$, for odd $c$ and $a = 10000k$, we have $S \equiv 0(\bmod 10000)$. So if $7989.7989 > {\left( {a - \sqrt b } \right)^c} > 7989.7988$, then we done. Let $b = {(a - 1)^2} - 1 = {a^2} - 2a$, then $\mathop {\lim }\limits_{a \to + \infty } a - \sqrt b = \mathop {\lim }\limits_{a \to + \infty } \frac{{2a}}{{a + \sqrt {a^2-2a} }} = 1$, so for large $k$, that we have $1 < a - \sqrt b < {\left( {\frac{{7989.7989}}{{7989.7988}}} \right)^{1/3000}}$. If $\alpha $ is the biggest integer for $7989.7988 \geqslant {\left( {a - \sqrt b } \right)^\alpha }$, then $\alpha > 3000$, and $7989.7988 < {\left( {a - \sqrt b } \right)^{\alpha + 1}}<{\left( {a - \sqrt b } \right)^{\alpha + 2}}<7989.7988 \times {\left( {\sqrt {\frac{{7989.7989}}{{7989.7988}}} } \right)^2}=7989.7989$. Let $c$ be the odd one of $\alpha+1, \alpha+2$, then $7989.7989 > {\left( {a - \sqrt b } \right)^c} > 7989.7988$. So $a,b,c>3000$, and ${\left( {a + \sqrt b } \right)^c}=S-{\left( {a - \sqrt b } \right)^c}= ...2010.2011...$.