Absolute Value Inequality (another)
$begingroup$
Solve the following inequality
$$|a-2| > |a+4|$$
Here I separated it into cases as shown
$a<-4$
$$-(a-2) > -(a+4) implies 2-a>-a-4 implies 0>-6$$
Always true, so we get $mathbb{R} cap (-infty , -4) = (-infty ,-4)$
$-4<a<2$
$$-(a-2)>a+4 implies 2-a>a+4 implies a<-1$$
Taking interception $(-4,2)$ $cap $ $(-infty,-1)$
$a>2$
$$a-2 > a+4 implies -2>4 $$
Always false, so no solution from there. Finally, I checked end points and noticed that they do not work in this inequality. However, I do not know how to proceed further. Could you assist me?
Regards
inequality
$endgroup$
add a comment |
$begingroup$
Solve the following inequality
$$|a-2| > |a+4|$$
Here I separated it into cases as shown
$a<-4$
$$-(a-2) > -(a+4) implies 2-a>-a-4 implies 0>-6$$
Always true, so we get $mathbb{R} cap (-infty , -4) = (-infty ,-4)$
$-4<a<2$
$$-(a-2)>a+4 implies 2-a>a+4 implies a<-1$$
Taking interception $(-4,2)$ $cap $ $(-infty,-1)$
$a>2$
$$a-2 > a+4 implies -2>4 $$
Always false, so no solution from there. Finally, I checked end points and noticed that they do not work in this inequality. However, I do not know how to proceed further. Could you assist me?
Regards
inequality
$endgroup$
$begingroup$
With $;a=4;$ your inequality is $$2=|4-2|>|4+4|=8...text{you still think this is true?}$$
$endgroup$
– DonAntonio
Jan 13 at 13:18
1
$begingroup$
@DonAntonio Not really, thanks for pointing out.
$endgroup$
– Enzo
Jan 13 at 13:19
add a comment |
$begingroup$
Solve the following inequality
$$|a-2| > |a+4|$$
Here I separated it into cases as shown
$a<-4$
$$-(a-2) > -(a+4) implies 2-a>-a-4 implies 0>-6$$
Always true, so we get $mathbb{R} cap (-infty , -4) = (-infty ,-4)$
$-4<a<2$
$$-(a-2)>a+4 implies 2-a>a+4 implies a<-1$$
Taking interception $(-4,2)$ $cap $ $(-infty,-1)$
$a>2$
$$a-2 > a+4 implies -2>4 $$
Always false, so no solution from there. Finally, I checked end points and noticed that they do not work in this inequality. However, I do not know how to proceed further. Could you assist me?
Regards
inequality
$endgroup$
Solve the following inequality
$$|a-2| > |a+4|$$
Here I separated it into cases as shown
$a<-4$
$$-(a-2) > -(a+4) implies 2-a>-a-4 implies 0>-6$$
Always true, so we get $mathbb{R} cap (-infty , -4) = (-infty ,-4)$
$-4<a<2$
$$-(a-2)>a+4 implies 2-a>a+4 implies a<-1$$
Taking interception $(-4,2)$ $cap $ $(-infty,-1)$
$a>2$
$$a-2 > a+4 implies -2>4 $$
Always false, so no solution from there. Finally, I checked end points and noticed that they do not work in this inequality. However, I do not know how to proceed further. Could you assist me?
Regards
inequality
inequality
edited Jan 13 at 13:34
Ethan Bolker
43.1k551114
43.1k551114
asked Jan 13 at 13:16
EnzoEnzo
19917
19917
$begingroup$
With $;a=4;$ your inequality is $$2=|4-2|>|4+4|=8...text{you still think this is true?}$$
$endgroup$
– DonAntonio
Jan 13 at 13:18
1
$begingroup$
@DonAntonio Not really, thanks for pointing out.
$endgroup$
– Enzo
Jan 13 at 13:19
add a comment |
$begingroup$
With $;a=4;$ your inequality is $$2=|4-2|>|4+4|=8...text{you still think this is true?}$$
$endgroup$
– DonAntonio
Jan 13 at 13:18
1
$begingroup$
@DonAntonio Not really, thanks for pointing out.
$endgroup$
– Enzo
Jan 13 at 13:19
$begingroup$
With $;a=4;$ your inequality is $$2=|4-2|>|4+4|=8...text{you still think this is true?}$$
$endgroup$
– DonAntonio
Jan 13 at 13:18
$begingroup$
With $;a=4;$ your inequality is $$2=|4-2|>|4+4|=8...text{you still think this is true?}$$
$endgroup$
– DonAntonio
Jan 13 at 13:18
1
1
$begingroup$
@DonAntonio Not really, thanks for pointing out.
$endgroup$
– Enzo
Jan 13 at 13:19
$begingroup$
@DonAntonio Not really, thanks for pointing out.
$endgroup$
– Enzo
Jan 13 at 13:19
add a comment |
4 Answers
4
active
oldest
votes
$begingroup$
As commented, $;a=4;$ doesn't really fits in the inequality. You can now put your solution set as
$$(-infty,-4)cupleft((-4,-2)cap(-infty,-1)right)=(-infty,-4)cup(-4,-1)=(-infty,-1)setminus{-4}$$
$endgroup$
$begingroup$
What does this mathematical symbol mean ?
$endgroup$
– Enzo
Jan 13 at 13:23
$begingroup$
Set difference. Sometimes it is also used $;A-B;$ ... A simple minus sign.
$endgroup$
– DonAntonio
Jan 13 at 13:23
$begingroup$
The right answer seems to be $(-infty, -1)$ according to my textbook. Do we get it from your final interval?:
$endgroup$
– Enzo
Jan 13 at 13:24
$begingroup$
That is correct, @Enzo . Your solution didn't even take into account $;a=-4;$ (perhaps you should have done this in the first case). That you have an inequality < or > doesn't mean you must take your cases in the same way
$endgroup$
– DonAntonio
Jan 13 at 13:34
add a comment |
$begingroup$
If you interpret the absolute values in terms of distance, it is immediate:
$|a-2|>|a+4|$ means $a$ is nearer to $-4$ than to $2$, so it is less than the arithmetic mean of $2$ and $-4$:
$$a<frac{2-4}2=-1$$
Other method:
begin{align}
|a-2|>|a+4|&iff(a-2)^2>(a+4)^2 \
&iff a^2-4a+4>a^2+8a+16\
&iff 12a+12<0iff a<-1.
end{align}
$endgroup$
add a comment |
$begingroup$
You have to distinguish the following cases:
$$xgeq 2$$ then we get $$x-2>x+4$$
$$-4le x<2$$ then we get $$x-2>-x+4$$
$$x<-4$$ then we have $$-x+2>-x-4$$
$endgroup$
add a comment |
$begingroup$
$|(a+1)-3|>|(a+1)+3|;$
$x:=a+1$;
$|x-(+3)| >|x-(-3)|;$
Real number line :
Distance from a point $x$ to $(+3)$ is bigger than from $x$
to $(-3)$, i.e. $x<0.$
(Note : At $x=0$ both distances are equal, for $x <0$, $x$ is to the left of $0$ , closer to $(-3)$ ).
$x= a+1<0$, $a<-1$.
$endgroup$
add a comment |
Your Answer
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4 Answers
4
active
oldest
votes
4 Answers
4
active
oldest
votes
active
oldest
votes
active
oldest
votes
$begingroup$
As commented, $;a=4;$ doesn't really fits in the inequality. You can now put your solution set as
$$(-infty,-4)cupleft((-4,-2)cap(-infty,-1)right)=(-infty,-4)cup(-4,-1)=(-infty,-1)setminus{-4}$$
$endgroup$
$begingroup$
What does this mathematical symbol mean ?
$endgroup$
– Enzo
Jan 13 at 13:23
$begingroup$
Set difference. Sometimes it is also used $;A-B;$ ... A simple minus sign.
$endgroup$
– DonAntonio
Jan 13 at 13:23
$begingroup$
The right answer seems to be $(-infty, -1)$ according to my textbook. Do we get it from your final interval?:
$endgroup$
– Enzo
Jan 13 at 13:24
$begingroup$
That is correct, @Enzo . Your solution didn't even take into account $;a=-4;$ (perhaps you should have done this in the first case). That you have an inequality < or > doesn't mean you must take your cases in the same way
$endgroup$
– DonAntonio
Jan 13 at 13:34
add a comment |
$begingroup$
As commented, $;a=4;$ doesn't really fits in the inequality. You can now put your solution set as
$$(-infty,-4)cupleft((-4,-2)cap(-infty,-1)right)=(-infty,-4)cup(-4,-1)=(-infty,-1)setminus{-4}$$
$endgroup$
$begingroup$
What does this mathematical symbol mean ?
$endgroup$
– Enzo
Jan 13 at 13:23
$begingroup$
Set difference. Sometimes it is also used $;A-B;$ ... A simple minus sign.
$endgroup$
– DonAntonio
Jan 13 at 13:23
$begingroup$
The right answer seems to be $(-infty, -1)$ according to my textbook. Do we get it from your final interval?:
$endgroup$
– Enzo
Jan 13 at 13:24
$begingroup$
That is correct, @Enzo . Your solution didn't even take into account $;a=-4;$ (perhaps you should have done this in the first case). That you have an inequality < or > doesn't mean you must take your cases in the same way
$endgroup$
– DonAntonio
Jan 13 at 13:34
add a comment |
$begingroup$
As commented, $;a=4;$ doesn't really fits in the inequality. You can now put your solution set as
$$(-infty,-4)cupleft((-4,-2)cap(-infty,-1)right)=(-infty,-4)cup(-4,-1)=(-infty,-1)setminus{-4}$$
$endgroup$
As commented, $;a=4;$ doesn't really fits in the inequality. You can now put your solution set as
$$(-infty,-4)cupleft((-4,-2)cap(-infty,-1)right)=(-infty,-4)cup(-4,-1)=(-infty,-1)setminus{-4}$$
answered Jan 13 at 13:22
DonAntonioDonAntonio
178k1494230
178k1494230
$begingroup$
What does this mathematical symbol mean ?
$endgroup$
– Enzo
Jan 13 at 13:23
$begingroup$
Set difference. Sometimes it is also used $;A-B;$ ... A simple minus sign.
$endgroup$
– DonAntonio
Jan 13 at 13:23
$begingroup$
The right answer seems to be $(-infty, -1)$ according to my textbook. Do we get it from your final interval?:
$endgroup$
– Enzo
Jan 13 at 13:24
$begingroup$
That is correct, @Enzo . Your solution didn't even take into account $;a=-4;$ (perhaps you should have done this in the first case). That you have an inequality < or > doesn't mean you must take your cases in the same way
$endgroup$
– DonAntonio
Jan 13 at 13:34
add a comment |
$begingroup$
What does this mathematical symbol mean ?
$endgroup$
– Enzo
Jan 13 at 13:23
$begingroup$
Set difference. Sometimes it is also used $;A-B;$ ... A simple minus sign.
$endgroup$
– DonAntonio
Jan 13 at 13:23
$begingroup$
The right answer seems to be $(-infty, -1)$ according to my textbook. Do we get it from your final interval?:
$endgroup$
– Enzo
Jan 13 at 13:24
$begingroup$
That is correct, @Enzo . Your solution didn't even take into account $;a=-4;$ (perhaps you should have done this in the first case). That you have an inequality < or > doesn't mean you must take your cases in the same way
$endgroup$
– DonAntonio
Jan 13 at 13:34
$begingroup$
What does this mathematical symbol mean ?
$endgroup$
– Enzo
Jan 13 at 13:23
$begingroup$
What does this mathematical symbol mean ?
$endgroup$
– Enzo
Jan 13 at 13:23
$begingroup$
Set difference. Sometimes it is also used $;A-B;$ ... A simple minus sign.
$endgroup$
– DonAntonio
Jan 13 at 13:23
$begingroup$
Set difference. Sometimes it is also used $;A-B;$ ... A simple minus sign.
$endgroup$
– DonAntonio
Jan 13 at 13:23
$begingroup$
The right answer seems to be $(-infty, -1)$ according to my textbook. Do we get it from your final interval?:
$endgroup$
– Enzo
Jan 13 at 13:24
$begingroup$
The right answer seems to be $(-infty, -1)$ according to my textbook. Do we get it from your final interval?:
$endgroup$
– Enzo
Jan 13 at 13:24
$begingroup$
That is correct, @Enzo . Your solution didn't even take into account $;a=-4;$ (perhaps you should have done this in the first case). That you have an inequality < or > doesn't mean you must take your cases in the same way
$endgroup$
– DonAntonio
Jan 13 at 13:34
$begingroup$
That is correct, @Enzo . Your solution didn't even take into account $;a=-4;$ (perhaps you should have done this in the first case). That you have an inequality < or > doesn't mean you must take your cases in the same way
$endgroup$
– DonAntonio
Jan 13 at 13:34
add a comment |
$begingroup$
If you interpret the absolute values in terms of distance, it is immediate:
$|a-2|>|a+4|$ means $a$ is nearer to $-4$ than to $2$, so it is less than the arithmetic mean of $2$ and $-4$:
$$a<frac{2-4}2=-1$$
Other method:
begin{align}
|a-2|>|a+4|&iff(a-2)^2>(a+4)^2 \
&iff a^2-4a+4>a^2+8a+16\
&iff 12a+12<0iff a<-1.
end{align}
$endgroup$
add a comment |
$begingroup$
If you interpret the absolute values in terms of distance, it is immediate:
$|a-2|>|a+4|$ means $a$ is nearer to $-4$ than to $2$, so it is less than the arithmetic mean of $2$ and $-4$:
$$a<frac{2-4}2=-1$$
Other method:
begin{align}
|a-2|>|a+4|&iff(a-2)^2>(a+4)^2 \
&iff a^2-4a+4>a^2+8a+16\
&iff 12a+12<0iff a<-1.
end{align}
$endgroup$
add a comment |
$begingroup$
If you interpret the absolute values in terms of distance, it is immediate:
$|a-2|>|a+4|$ means $a$ is nearer to $-4$ than to $2$, so it is less than the arithmetic mean of $2$ and $-4$:
$$a<frac{2-4}2=-1$$
Other method:
begin{align}
|a-2|>|a+4|&iff(a-2)^2>(a+4)^2 \
&iff a^2-4a+4>a^2+8a+16\
&iff 12a+12<0iff a<-1.
end{align}
$endgroup$
If you interpret the absolute values in terms of distance, it is immediate:
$|a-2|>|a+4|$ means $a$ is nearer to $-4$ than to $2$, so it is less than the arithmetic mean of $2$ and $-4$:
$$a<frac{2-4}2=-1$$
Other method:
begin{align}
|a-2|>|a+4|&iff(a-2)^2>(a+4)^2 \
&iff a^2-4a+4>a^2+8a+16\
&iff 12a+12<0iff a<-1.
end{align}
edited Jan 13 at 13:51
answered Jan 13 at 13:42
BernardBernard
121k740116
121k740116
add a comment |
add a comment |
$begingroup$
You have to distinguish the following cases:
$$xgeq 2$$ then we get $$x-2>x+4$$
$$-4le x<2$$ then we get $$x-2>-x+4$$
$$x<-4$$ then we have $$-x+2>-x-4$$
$endgroup$
add a comment |
$begingroup$
You have to distinguish the following cases:
$$xgeq 2$$ then we get $$x-2>x+4$$
$$-4le x<2$$ then we get $$x-2>-x+4$$
$$x<-4$$ then we have $$-x+2>-x-4$$
$endgroup$
add a comment |
$begingroup$
You have to distinguish the following cases:
$$xgeq 2$$ then we get $$x-2>x+4$$
$$-4le x<2$$ then we get $$x-2>-x+4$$
$$x<-4$$ then we have $$-x+2>-x-4$$
$endgroup$
You have to distinguish the following cases:
$$xgeq 2$$ then we get $$x-2>x+4$$
$$-4le x<2$$ then we get $$x-2>-x+4$$
$$x<-4$$ then we have $$-x+2>-x-4$$
answered Jan 13 at 13:20
Dr. Sonnhard GraubnerDr. Sonnhard Graubner
75.3k42865
75.3k42865
add a comment |
add a comment |
$begingroup$
$|(a+1)-3|>|(a+1)+3|;$
$x:=a+1$;
$|x-(+3)| >|x-(-3)|;$
Real number line :
Distance from a point $x$ to $(+3)$ is bigger than from $x$
to $(-3)$, i.e. $x<0.$
(Note : At $x=0$ both distances are equal, for $x <0$, $x$ is to the left of $0$ , closer to $(-3)$ ).
$x= a+1<0$, $a<-1$.
$endgroup$
add a comment |
$begingroup$
$|(a+1)-3|>|(a+1)+3|;$
$x:=a+1$;
$|x-(+3)| >|x-(-3)|;$
Real number line :
Distance from a point $x$ to $(+3)$ is bigger than from $x$
to $(-3)$, i.e. $x<0.$
(Note : At $x=0$ both distances are equal, for $x <0$, $x$ is to the left of $0$ , closer to $(-3)$ ).
$x= a+1<0$, $a<-1$.
$endgroup$
add a comment |
$begingroup$
$|(a+1)-3|>|(a+1)+3|;$
$x:=a+1$;
$|x-(+3)| >|x-(-3)|;$
Real number line :
Distance from a point $x$ to $(+3)$ is bigger than from $x$
to $(-3)$, i.e. $x<0.$
(Note : At $x=0$ both distances are equal, for $x <0$, $x$ is to the left of $0$ , closer to $(-3)$ ).
$x= a+1<0$, $a<-1$.
$endgroup$
$|(a+1)-3|>|(a+1)+3|;$
$x:=a+1$;
$|x-(+3)| >|x-(-3)|;$
Real number line :
Distance from a point $x$ to $(+3)$ is bigger than from $x$
to $(-3)$, i.e. $x<0.$
(Note : At $x=0$ both distances are equal, for $x <0$, $x$ is to the left of $0$ , closer to $(-3)$ ).
$x= a+1<0$, $a<-1$.
answered Jan 13 at 16:14
Peter SzilasPeter Szilas
11.3k2822
11.3k2822
add a comment |
add a comment |
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$begingroup$
With $;a=4;$ your inequality is $$2=|4-2|>|4+4|=8...text{you still think this is true?}$$
$endgroup$
– DonAntonio
Jan 13 at 13:18
1
$begingroup$
@DonAntonio Not really, thanks for pointing out.
$endgroup$
– Enzo
Jan 13 at 13:19