Does this inequality make sense? 1 = |1|?
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-1
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Okay so suppose x = -9.
Then we have x < 1 .
But 1 = |1|
Hence x < |1|
Implies -1 < x < 1
But this clearly is not true.
Just wondering what the limitations are when using inequalities or is there a limitation with the absolute value. Or am I just missing something?
Also I wondered. If x< 4 and x > 4, can we say x = 4?
real-analysis algebra-precalculus inequality
add a comment |
up vote
-1
down vote
favorite
Okay so suppose x = -9.
Then we have x < 1 .
But 1 = |1|
Hence x < |1|
Implies -1 < x < 1
But this clearly is not true.
Just wondering what the limitations are when using inequalities or is there a limitation with the absolute value. Or am I just missing something?
Also I wondered. If x< 4 and x > 4, can we say x = 4?
real-analysis algebra-precalculus inequality
3
"x < |1| Implies -1 < x < 1" No it doesn't. $|x|<1$ implies $-1<x<1$.
– Rahul
Nov 18 at 10:39
Ahhhhhhh i am so silly! xD
– Sashin Chetty
Nov 19 at 13:34
add a comment |
up vote
-1
down vote
favorite
up vote
-1
down vote
favorite
Okay so suppose x = -9.
Then we have x < 1 .
But 1 = |1|
Hence x < |1|
Implies -1 < x < 1
But this clearly is not true.
Just wondering what the limitations are when using inequalities or is there a limitation with the absolute value. Or am I just missing something?
Also I wondered. If x< 4 and x > 4, can we say x = 4?
real-analysis algebra-precalculus inequality
Okay so suppose x = -9.
Then we have x < 1 .
But 1 = |1|
Hence x < |1|
Implies -1 < x < 1
But this clearly is not true.
Just wondering what the limitations are when using inequalities or is there a limitation with the absolute value. Or am I just missing something?
Also I wondered. If x< 4 and x > 4, can we say x = 4?
real-analysis algebra-precalculus inequality
real-analysis algebra-precalculus inequality
asked Nov 18 at 10:33
Sashin Chetty
222
222
3
"x < |1| Implies -1 < x < 1" No it doesn't. $|x|<1$ implies $-1<x<1$.
– Rahul
Nov 18 at 10:39
Ahhhhhhh i am so silly! xD
– Sashin Chetty
Nov 19 at 13:34
add a comment |
3
"x < |1| Implies -1 < x < 1" No it doesn't. $|x|<1$ implies $-1<x<1$.
– Rahul
Nov 18 at 10:39
Ahhhhhhh i am so silly! xD
– Sashin Chetty
Nov 19 at 13:34
3
3
"x < |1| Implies -1 < x < 1" No it doesn't. $|x|<1$ implies $-1<x<1$.
– Rahul
Nov 18 at 10:39
"x < |1| Implies -1 < x < 1" No it doesn't. $|x|<1$ implies $-1<x<1$.
– Rahul
Nov 18 at 10:39
Ahhhhhhh i am so silly! xD
– Sashin Chetty
Nov 19 at 13:34
Ahhhhhhh i am so silly! xD
– Sashin Chetty
Nov 19 at 13:34
add a comment |
3 Answers
3
active
oldest
votes
up vote
1
down vote
You are confusing $|x| < 1$ with $x < |1|$.
when $x=-9$, the first inequality that I have written above is not true.
Also, there is no number that satisfies $x<4$ and $x > 4$.
However, if $x le 4$ and $x ge 4$, then we can say that $x=4$.
add a comment |
up vote
1
down vote
There is some confusion here. It is not true that $x<lvert1rvertimplies-1<x<1$. Perhaps that you are thinking about $lvert xrvert<1implies-1<x<1$.
And if $x<4$ and $x>4$, then there is no such $x$. In particular, you can't say that $x=4$.
add a comment |
up vote
0
down vote
You seem to be assuming that if $a<b$ then $|a|<|b|$, but that is not true. More generally, if $a<b$ that does not necessarily imply $f(a)<f(b)$ for any function $f$. However, it is true if $f$ is strictly increasing (which the absolute value function isn't).
If $x<|1|$ that is the same as saying $x<1$ because the absolute value of 1 is simply 1. However, If $|x|<1$ then it is true that $-1<x<1$.
If $x<4$ and $x>4$ then $x$ does not exist, because no real number satisfies both of those conditions.
add a comment |
3 Answers
3
active
oldest
votes
3 Answers
3
active
oldest
votes
active
oldest
votes
active
oldest
votes
up vote
1
down vote
You are confusing $|x| < 1$ with $x < |1|$.
when $x=-9$, the first inequality that I have written above is not true.
Also, there is no number that satisfies $x<4$ and $x > 4$.
However, if $x le 4$ and $x ge 4$, then we can say that $x=4$.
add a comment |
up vote
1
down vote
You are confusing $|x| < 1$ with $x < |1|$.
when $x=-9$, the first inequality that I have written above is not true.
Also, there is no number that satisfies $x<4$ and $x > 4$.
However, if $x le 4$ and $x ge 4$, then we can say that $x=4$.
add a comment |
up vote
1
down vote
up vote
1
down vote
You are confusing $|x| < 1$ with $x < |1|$.
when $x=-9$, the first inequality that I have written above is not true.
Also, there is no number that satisfies $x<4$ and $x > 4$.
However, if $x le 4$ and $x ge 4$, then we can say that $x=4$.
You are confusing $|x| < 1$ with $x < |1|$.
when $x=-9$, the first inequality that I have written above is not true.
Also, there is no number that satisfies $x<4$ and $x > 4$.
However, if $x le 4$ and $x ge 4$, then we can say that $x=4$.
answered Nov 18 at 10:38
Siong Thye Goh
95.9k1462116
95.9k1462116
add a comment |
add a comment |
up vote
1
down vote
There is some confusion here. It is not true that $x<lvert1rvertimplies-1<x<1$. Perhaps that you are thinking about $lvert xrvert<1implies-1<x<1$.
And if $x<4$ and $x>4$, then there is no such $x$. In particular, you can't say that $x=4$.
add a comment |
up vote
1
down vote
There is some confusion here. It is not true that $x<lvert1rvertimplies-1<x<1$. Perhaps that you are thinking about $lvert xrvert<1implies-1<x<1$.
And if $x<4$ and $x>4$, then there is no such $x$. In particular, you can't say that $x=4$.
add a comment |
up vote
1
down vote
up vote
1
down vote
There is some confusion here. It is not true that $x<lvert1rvertimplies-1<x<1$. Perhaps that you are thinking about $lvert xrvert<1implies-1<x<1$.
And if $x<4$ and $x>4$, then there is no such $x$. In particular, you can't say that $x=4$.
There is some confusion here. It is not true that $x<lvert1rvertimplies-1<x<1$. Perhaps that you are thinking about $lvert xrvert<1implies-1<x<1$.
And if $x<4$ and $x>4$, then there is no such $x$. In particular, you can't say that $x=4$.
answered Nov 18 at 10:39
José Carlos Santos
143k20112212
143k20112212
add a comment |
add a comment |
up vote
0
down vote
You seem to be assuming that if $a<b$ then $|a|<|b|$, but that is not true. More generally, if $a<b$ that does not necessarily imply $f(a)<f(b)$ for any function $f$. However, it is true if $f$ is strictly increasing (which the absolute value function isn't).
If $x<|1|$ that is the same as saying $x<1$ because the absolute value of 1 is simply 1. However, If $|x|<1$ then it is true that $-1<x<1$.
If $x<4$ and $x>4$ then $x$ does not exist, because no real number satisfies both of those conditions.
add a comment |
up vote
0
down vote
You seem to be assuming that if $a<b$ then $|a|<|b|$, but that is not true. More generally, if $a<b$ that does not necessarily imply $f(a)<f(b)$ for any function $f$. However, it is true if $f$ is strictly increasing (which the absolute value function isn't).
If $x<|1|$ that is the same as saying $x<1$ because the absolute value of 1 is simply 1. However, If $|x|<1$ then it is true that $-1<x<1$.
If $x<4$ and $x>4$ then $x$ does not exist, because no real number satisfies both of those conditions.
add a comment |
up vote
0
down vote
up vote
0
down vote
You seem to be assuming that if $a<b$ then $|a|<|b|$, but that is not true. More generally, if $a<b$ that does not necessarily imply $f(a)<f(b)$ for any function $f$. However, it is true if $f$ is strictly increasing (which the absolute value function isn't).
If $x<|1|$ that is the same as saying $x<1$ because the absolute value of 1 is simply 1. However, If $|x|<1$ then it is true that $-1<x<1$.
If $x<4$ and $x>4$ then $x$ does not exist, because no real number satisfies both of those conditions.
You seem to be assuming that if $a<b$ then $|a|<|b|$, but that is not true. More generally, if $a<b$ that does not necessarily imply $f(a)<f(b)$ for any function $f$. However, it is true if $f$ is strictly increasing (which the absolute value function isn't).
If $x<|1|$ that is the same as saying $x<1$ because the absolute value of 1 is simply 1. However, If $|x|<1$ then it is true that $-1<x<1$.
If $x<4$ and $x>4$ then $x$ does not exist, because no real number satisfies both of those conditions.
answered Nov 18 at 10:39
Eff
11.5k21638
11.5k21638
add a comment |
add a comment |
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3
"x < |1| Implies -1 < x < 1" No it doesn't. $|x|<1$ implies $-1<x<1$.
– Rahul
Nov 18 at 10:39
Ahhhhhhh i am so silly! xD
– Sashin Chetty
Nov 19 at 13:34