Ceil and floor function
$begingroup$
Let $a$ and $b$ be positive integers.
If $b$ is even, then we have $$leftlfloor frac{a-b}{2} rightrfloor + leftlceil frac{a+b}{2} rightrceil = a$$
I thing the equality also hold when $b$ is odd. What could be a proof for it?
Thank you
floor-function ceiling-function
$endgroup$
add a comment |
$begingroup$
Let $a$ and $b$ be positive integers.
If $b$ is even, then we have $$leftlfloor frac{a-b}{2} rightrfloor + leftlceil frac{a+b}{2} rightrceil = a$$
I thing the equality also hold when $b$ is odd. What could be a proof for it?
Thank you
floor-function ceiling-function
$endgroup$
$begingroup$
Write $b$ as $2k + 1$, where $k$ is a nonnegative integer. Then look at two cases: $a = 2s$ ($s$ a positive integer), and $a = 2s + 1$ ($s$ a nonnegative integer). What do you get for the left-hand side in each case? [You can show your work by clicking "edit" beneath your question.]
$endgroup$
– John Hughes
22 mins ago
add a comment |
$begingroup$
Let $a$ and $b$ be positive integers.
If $b$ is even, then we have $$leftlfloor frac{a-b}{2} rightrfloor + leftlceil frac{a+b}{2} rightrceil = a$$
I thing the equality also hold when $b$ is odd. What could be a proof for it?
Thank you
floor-function ceiling-function
$endgroup$
Let $a$ and $b$ be positive integers.
If $b$ is even, then we have $$leftlfloor frac{a-b}{2} rightrfloor + leftlceil frac{a+b}{2} rightrceil = a$$
I thing the equality also hold when $b$ is odd. What could be a proof for it?
Thank you
floor-function ceiling-function
floor-function ceiling-function
edited 26 mins ago
Adam54
asked 31 mins ago
Adam54Adam54
615
615
$begingroup$
Write $b$ as $2k + 1$, where $k$ is a nonnegative integer. Then look at two cases: $a = 2s$ ($s$ a positive integer), and $a = 2s + 1$ ($s$ a nonnegative integer). What do you get for the left-hand side in each case? [You can show your work by clicking "edit" beneath your question.]
$endgroup$
– John Hughes
22 mins ago
add a comment |
$begingroup$
Write $b$ as $2k + 1$, where $k$ is a nonnegative integer. Then look at two cases: $a = 2s$ ($s$ a positive integer), and $a = 2s + 1$ ($s$ a nonnegative integer). What do you get for the left-hand side in each case? [You can show your work by clicking "edit" beneath your question.]
$endgroup$
– John Hughes
22 mins ago
$begingroup$
Write $b$ as $2k + 1$, where $k$ is a nonnegative integer. Then look at two cases: $a = 2s$ ($s$ a positive integer), and $a = 2s + 1$ ($s$ a nonnegative integer). What do you get for the left-hand side in each case? [You can show your work by clicking "edit" beneath your question.]
$endgroup$
– John Hughes
22 mins ago
$begingroup$
Write $b$ as $2k + 1$, where $k$ is a nonnegative integer. Then look at two cases: $a = 2s$ ($s$ a positive integer), and $a = 2s + 1$ ($s$ a nonnegative integer). What do you get for the left-hand side in each case? [You can show your work by clicking "edit" beneath your question.]
$endgroup$
– John Hughes
22 mins ago
add a comment |
4 Answers
4
active
oldest
votes
$begingroup$
If $a$ and $b$ are both odd (or both even), then $a-b$ and $a+b$ are both even, and thus $$leftlfloor frac{a-b}{2} rightrfloor = frac{a-b}{2} quadtext{and}quad leftlceil frac{a+b}{2} rightrceil = frac{a+b}{2}.$$
Otherwise, if exactly one of $a$ and $b$ is odd, then $a-b$ and $a+b$ are both odd, and thus $$leftlfloor frac{a-b}{2} rightrfloor = frac{a-b}{2} - frac12 quadtext{and}quad leftlceil frac{a+b}{2} rightrceil = frac{a+b}{2} + frac12.$$
In either case, it's easy to check that your equation holds.
$endgroup$
$begingroup$
Thank you very much for the odd case, made very simple!
$endgroup$
– Adam54
14 mins ago
add a comment |
$begingroup$
The equality only depends on the parity of $a+b$, as it is the same as that of $a-b$. Then
$$leftlfloorfrac02rightrfloor+leftlceilfrac02rightrceil=0$$
and
$$leftlfloorfrac12rightrfloor+leftlceilfrac12rightrceil=1$$
are enough as a proof.
$endgroup$
add a comment |
$begingroup$
If $a$ and $b$ are both odd then we have $a=2m+1$ and $b=2n+1$ where $m$ and $n$ are positive integers.
Then, we have begin{align}leftlfloorfrac{a-b}2rightrfloor+leftlceilfrac{a+b}2rightrceil &= leftlfloorfrac{(2m+1)-(2n+1)}2rightrfloor+ leftlceilfrac{(2m+1)+(2n+1)}2rightrceil\
&=leftlfloorfrac{2m-2n}2rightrfloor+ leftlceilfrac{2m+2n+2}2rightrceil\
&=lfloor m-nrfloor + lceil m+n+1rceil\
&= m-n + m+n+1tag{$*$}\
&= 2m+1\
&=aend{align}
We can get to $(*)$ because $m$ and $n$ are integers and so their floor (or ceiling) is just the number inside (two integers added or subtracted will always give an integer answer).
If $a$ is even and $b$ is odd, then we have $a=2m$ and $b=2n+1$, again for $m$ and $n$ integers.
So we have begin{align}leftlfloorfrac{a-b}2rightrfloor+leftlceilfrac{a+b}2rightrceil &= leftlfloorfrac{(2m)-(2n+1)}2rightrfloor+ leftlceilfrac{(2m)+(2n+1)}2rightrceil\
&=leftlfloorfrac{2m-2n-1}2rightrfloor+ leftlceilfrac{2m+2n+1}2rightrceil\
&=leftlfloor m-n-frac 12rightrfloor + leftlceil m+n+frac12rightrceil\
&= m-n -1+ m+n+1tag{$dagger$}\
&= 2m\
&=aend{align}
Here we get to $(dagger)$ because we round the first half down and the second half up to their respective nearest integers
$endgroup$
add a comment |
$begingroup$
As $s:=a+b$ and $a-b$ have the same parity, we can write
$$leftlfloorfrac{s-2b}2rightrfloor+leftlceilfrac s2rightrceil=leftlfloorfrac s2rightrfloor+leftlceilfrac s2rightrceil-b=s-b=a.$$
$endgroup$
add a comment |
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4 Answers
4
active
oldest
votes
4 Answers
4
active
oldest
votes
active
oldest
votes
active
oldest
votes
$begingroup$
If $a$ and $b$ are both odd (or both even), then $a-b$ and $a+b$ are both even, and thus $$leftlfloor frac{a-b}{2} rightrfloor = frac{a-b}{2} quadtext{and}quad leftlceil frac{a+b}{2} rightrceil = frac{a+b}{2}.$$
Otherwise, if exactly one of $a$ and $b$ is odd, then $a-b$ and $a+b$ are both odd, and thus $$leftlfloor frac{a-b}{2} rightrfloor = frac{a-b}{2} - frac12 quadtext{and}quad leftlceil frac{a+b}{2} rightrceil = frac{a+b}{2} + frac12.$$
In either case, it's easy to check that your equation holds.
$endgroup$
$begingroup$
Thank you very much for the odd case, made very simple!
$endgroup$
– Adam54
14 mins ago
add a comment |
$begingroup$
If $a$ and $b$ are both odd (or both even), then $a-b$ and $a+b$ are both even, and thus $$leftlfloor frac{a-b}{2} rightrfloor = frac{a-b}{2} quadtext{and}quad leftlceil frac{a+b}{2} rightrceil = frac{a+b}{2}.$$
Otherwise, if exactly one of $a$ and $b$ is odd, then $a-b$ and $a+b$ are both odd, and thus $$leftlfloor frac{a-b}{2} rightrfloor = frac{a-b}{2} - frac12 quadtext{and}quad leftlceil frac{a+b}{2} rightrceil = frac{a+b}{2} + frac12.$$
In either case, it's easy to check that your equation holds.
$endgroup$
$begingroup$
Thank you very much for the odd case, made very simple!
$endgroup$
– Adam54
14 mins ago
add a comment |
$begingroup$
If $a$ and $b$ are both odd (or both even), then $a-b$ and $a+b$ are both even, and thus $$leftlfloor frac{a-b}{2} rightrfloor = frac{a-b}{2} quadtext{and}quad leftlceil frac{a+b}{2} rightrceil = frac{a+b}{2}.$$
Otherwise, if exactly one of $a$ and $b$ is odd, then $a-b$ and $a+b$ are both odd, and thus $$leftlfloor frac{a-b}{2} rightrfloor = frac{a-b}{2} - frac12 quadtext{and}quad leftlceil frac{a+b}{2} rightrceil = frac{a+b}{2} + frac12.$$
In either case, it's easy to check that your equation holds.
$endgroup$
If $a$ and $b$ are both odd (or both even), then $a-b$ and $a+b$ are both even, and thus $$leftlfloor frac{a-b}{2} rightrfloor = frac{a-b}{2} quadtext{and}quad leftlceil frac{a+b}{2} rightrceil = frac{a+b}{2}.$$
Otherwise, if exactly one of $a$ and $b$ is odd, then $a-b$ and $a+b$ are both odd, and thus $$leftlfloor frac{a-b}{2} rightrfloor = frac{a-b}{2} - frac12 quadtext{and}quad leftlceil frac{a+b}{2} rightrceil = frac{a+b}{2} + frac12.$$
In either case, it's easy to check that your equation holds.
answered 17 mins ago
Ilmari KaronenIlmari Karonen
19.7k25183
19.7k25183
$begingroup$
Thank you very much for the odd case, made very simple!
$endgroup$
– Adam54
14 mins ago
add a comment |
$begingroup$
Thank you very much for the odd case, made very simple!
$endgroup$
– Adam54
14 mins ago
$begingroup$
Thank you very much for the odd case, made very simple!
$endgroup$
– Adam54
14 mins ago
$begingroup$
Thank you very much for the odd case, made very simple!
$endgroup$
– Adam54
14 mins ago
add a comment |
$begingroup$
The equality only depends on the parity of $a+b$, as it is the same as that of $a-b$. Then
$$leftlfloorfrac02rightrfloor+leftlceilfrac02rightrceil=0$$
and
$$leftlfloorfrac12rightrfloor+leftlceilfrac12rightrceil=1$$
are enough as a proof.
$endgroup$
add a comment |
$begingroup$
The equality only depends on the parity of $a+b$, as it is the same as that of $a-b$. Then
$$leftlfloorfrac02rightrfloor+leftlceilfrac02rightrceil=0$$
and
$$leftlfloorfrac12rightrfloor+leftlceilfrac12rightrceil=1$$
are enough as a proof.
$endgroup$
add a comment |
$begingroup$
The equality only depends on the parity of $a+b$, as it is the same as that of $a-b$. Then
$$leftlfloorfrac02rightrfloor+leftlceilfrac02rightrceil=0$$
and
$$leftlfloorfrac12rightrfloor+leftlceilfrac12rightrceil=1$$
are enough as a proof.
$endgroup$
The equality only depends on the parity of $a+b$, as it is the same as that of $a-b$. Then
$$leftlfloorfrac02rightrfloor+leftlceilfrac02rightrceil=0$$
and
$$leftlfloorfrac12rightrfloor+leftlceilfrac12rightrceil=1$$
are enough as a proof.
answered 19 mins ago
Yves DaoustYves Daoust
125k671223
125k671223
add a comment |
add a comment |
$begingroup$
If $a$ and $b$ are both odd then we have $a=2m+1$ and $b=2n+1$ where $m$ and $n$ are positive integers.
Then, we have begin{align}leftlfloorfrac{a-b}2rightrfloor+leftlceilfrac{a+b}2rightrceil &= leftlfloorfrac{(2m+1)-(2n+1)}2rightrfloor+ leftlceilfrac{(2m+1)+(2n+1)}2rightrceil\
&=leftlfloorfrac{2m-2n}2rightrfloor+ leftlceilfrac{2m+2n+2}2rightrceil\
&=lfloor m-nrfloor + lceil m+n+1rceil\
&= m-n + m+n+1tag{$*$}\
&= 2m+1\
&=aend{align}
We can get to $(*)$ because $m$ and $n$ are integers and so their floor (or ceiling) is just the number inside (two integers added or subtracted will always give an integer answer).
If $a$ is even and $b$ is odd, then we have $a=2m$ and $b=2n+1$, again for $m$ and $n$ integers.
So we have begin{align}leftlfloorfrac{a-b}2rightrfloor+leftlceilfrac{a+b}2rightrceil &= leftlfloorfrac{(2m)-(2n+1)}2rightrfloor+ leftlceilfrac{(2m)+(2n+1)}2rightrceil\
&=leftlfloorfrac{2m-2n-1}2rightrfloor+ leftlceilfrac{2m+2n+1}2rightrceil\
&=leftlfloor m-n-frac 12rightrfloor + leftlceil m+n+frac12rightrceil\
&= m-n -1+ m+n+1tag{$dagger$}\
&= 2m\
&=aend{align}
Here we get to $(dagger)$ because we round the first half down and the second half up to their respective nearest integers
$endgroup$
add a comment |
$begingroup$
If $a$ and $b$ are both odd then we have $a=2m+1$ and $b=2n+1$ where $m$ and $n$ are positive integers.
Then, we have begin{align}leftlfloorfrac{a-b}2rightrfloor+leftlceilfrac{a+b}2rightrceil &= leftlfloorfrac{(2m+1)-(2n+1)}2rightrfloor+ leftlceilfrac{(2m+1)+(2n+1)}2rightrceil\
&=leftlfloorfrac{2m-2n}2rightrfloor+ leftlceilfrac{2m+2n+2}2rightrceil\
&=lfloor m-nrfloor + lceil m+n+1rceil\
&= m-n + m+n+1tag{$*$}\
&= 2m+1\
&=aend{align}
We can get to $(*)$ because $m$ and $n$ are integers and so their floor (or ceiling) is just the number inside (two integers added or subtracted will always give an integer answer).
If $a$ is even and $b$ is odd, then we have $a=2m$ and $b=2n+1$, again for $m$ and $n$ integers.
So we have begin{align}leftlfloorfrac{a-b}2rightrfloor+leftlceilfrac{a+b}2rightrceil &= leftlfloorfrac{(2m)-(2n+1)}2rightrfloor+ leftlceilfrac{(2m)+(2n+1)}2rightrceil\
&=leftlfloorfrac{2m-2n-1}2rightrfloor+ leftlceilfrac{2m+2n+1}2rightrceil\
&=leftlfloor m-n-frac 12rightrfloor + leftlceil m+n+frac12rightrceil\
&= m-n -1+ m+n+1tag{$dagger$}\
&= 2m\
&=aend{align}
Here we get to $(dagger)$ because we round the first half down and the second half up to their respective nearest integers
$endgroup$
add a comment |
$begingroup$
If $a$ and $b$ are both odd then we have $a=2m+1$ and $b=2n+1$ where $m$ and $n$ are positive integers.
Then, we have begin{align}leftlfloorfrac{a-b}2rightrfloor+leftlceilfrac{a+b}2rightrceil &= leftlfloorfrac{(2m+1)-(2n+1)}2rightrfloor+ leftlceilfrac{(2m+1)+(2n+1)}2rightrceil\
&=leftlfloorfrac{2m-2n}2rightrfloor+ leftlceilfrac{2m+2n+2}2rightrceil\
&=lfloor m-nrfloor + lceil m+n+1rceil\
&= m-n + m+n+1tag{$*$}\
&= 2m+1\
&=aend{align}
We can get to $(*)$ because $m$ and $n$ are integers and so their floor (or ceiling) is just the number inside (two integers added or subtracted will always give an integer answer).
If $a$ is even and $b$ is odd, then we have $a=2m$ and $b=2n+1$, again for $m$ and $n$ integers.
So we have begin{align}leftlfloorfrac{a-b}2rightrfloor+leftlceilfrac{a+b}2rightrceil &= leftlfloorfrac{(2m)-(2n+1)}2rightrfloor+ leftlceilfrac{(2m)+(2n+1)}2rightrceil\
&=leftlfloorfrac{2m-2n-1}2rightrfloor+ leftlceilfrac{2m+2n+1}2rightrceil\
&=leftlfloor m-n-frac 12rightrfloor + leftlceil m+n+frac12rightrceil\
&= m-n -1+ m+n+1tag{$dagger$}\
&= 2m\
&=aend{align}
Here we get to $(dagger)$ because we round the first half down and the second half up to their respective nearest integers
$endgroup$
If $a$ and $b$ are both odd then we have $a=2m+1$ and $b=2n+1$ where $m$ and $n$ are positive integers.
Then, we have begin{align}leftlfloorfrac{a-b}2rightrfloor+leftlceilfrac{a+b}2rightrceil &= leftlfloorfrac{(2m+1)-(2n+1)}2rightrfloor+ leftlceilfrac{(2m+1)+(2n+1)}2rightrceil\
&=leftlfloorfrac{2m-2n}2rightrfloor+ leftlceilfrac{2m+2n+2}2rightrceil\
&=lfloor m-nrfloor + lceil m+n+1rceil\
&= m-n + m+n+1tag{$*$}\
&= 2m+1\
&=aend{align}
We can get to $(*)$ because $m$ and $n$ are integers and so their floor (or ceiling) is just the number inside (two integers added or subtracted will always give an integer answer).
If $a$ is even and $b$ is odd, then we have $a=2m$ and $b=2n+1$, again for $m$ and $n$ integers.
So we have begin{align}leftlfloorfrac{a-b}2rightrfloor+leftlceilfrac{a+b}2rightrceil &= leftlfloorfrac{(2m)-(2n+1)}2rightrfloor+ leftlceilfrac{(2m)+(2n+1)}2rightrceil\
&=leftlfloorfrac{2m-2n-1}2rightrfloor+ leftlceilfrac{2m+2n+1}2rightrceil\
&=leftlfloor m-n-frac 12rightrfloor + leftlceil m+n+frac12rightrceil\
&= m-n -1+ m+n+1tag{$dagger$}\
&= 2m\
&=aend{align}
Here we get to $(dagger)$ because we round the first half down and the second half up to their respective nearest integers
answered 16 mins ago
lioness99alioness99a
3,6842727
3,6842727
add a comment |
add a comment |
$begingroup$
As $s:=a+b$ and $a-b$ have the same parity, we can write
$$leftlfloorfrac{s-2b}2rightrfloor+leftlceilfrac s2rightrceil=leftlfloorfrac s2rightrfloor+leftlceilfrac s2rightrceil-b=s-b=a.$$
$endgroup$
add a comment |
$begingroup$
As $s:=a+b$ and $a-b$ have the same parity, we can write
$$leftlfloorfrac{s-2b}2rightrfloor+leftlceilfrac s2rightrceil=leftlfloorfrac s2rightrfloor+leftlceilfrac s2rightrceil-b=s-b=a.$$
$endgroup$
add a comment |
$begingroup$
As $s:=a+b$ and $a-b$ have the same parity, we can write
$$leftlfloorfrac{s-2b}2rightrfloor+leftlceilfrac s2rightrceil=leftlfloorfrac s2rightrfloor+leftlceilfrac s2rightrceil-b=s-b=a.$$
$endgroup$
As $s:=a+b$ and $a-b$ have the same parity, we can write
$$leftlfloorfrac{s-2b}2rightrfloor+leftlceilfrac s2rightrceil=leftlfloorfrac s2rightrfloor+leftlceilfrac s2rightrceil-b=s-b=a.$$
answered 4 mins ago
Yves DaoustYves Daoust
125k671223
125k671223
add a comment |
add a comment |
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$begingroup$
Write $b$ as $2k + 1$, where $k$ is a nonnegative integer. Then look at two cases: $a = 2s$ ($s$ a positive integer), and $a = 2s + 1$ ($s$ a nonnegative integer). What do you get for the left-hand side in each case? [You can show your work by clicking "edit" beneath your question.]
$endgroup$
– John Hughes
22 mins ago