AMC 1834 - If $a, b $ and $c$ are nonzero numbers such that (a+b-c)/c=(a-b+c)/b=(-a+b+c)/a and...
$begingroup$
I am getting stuck on this question:
If a, b, and c, are nonzero numbers such that $frac{a+b-c}{c}$=$frac{a-b+c}{b}$=$frac{-a+b+c}{a}$ and x=$frac{(a+b)(b+c)(c+a)}{abc}$ and x<0, then x=?
What I have done so far: Consider, if $frac{a}{b}$=$frac{c}{d}$, and (b+d) is non-zero, then $frac{a+c}{b+d}$=$frac{a}{b}$=$frac{c}{d}$. So with that fact, I did... $frac{a+b-c}{c}$=$frac{a-b+c}{b}$ $implies$
$frac{2a}{c+b}$ and $frac{2a}{c+b}$=$frac{-a+b+c}{a}$$implies$ $frac{(a+b+c)}{a+b+c}$ = 1. Then I took the original equations and did $frac{a+b-c}{c}$=1, so $a+b=2c$ , and similarly, $(a+c)=2b$ and $b+c=2a$. So plugging that into x=$frac{(a+b)(b+c)(c+a)}{abc}$ we have $x=frac{(2a)(2b)(2c)}{abc}$, which is $x=frac{8(abc)}{abc}=8$. This is wrong though, because it says in the problem x<0. So how do I do this?
algebra-precalculus fractions
$endgroup$
add a comment |
$begingroup$
I am getting stuck on this question:
If a, b, and c, are nonzero numbers such that $frac{a+b-c}{c}$=$frac{a-b+c}{b}$=$frac{-a+b+c}{a}$ and x=$frac{(a+b)(b+c)(c+a)}{abc}$ and x<0, then x=?
What I have done so far: Consider, if $frac{a}{b}$=$frac{c}{d}$, and (b+d) is non-zero, then $frac{a+c}{b+d}$=$frac{a}{b}$=$frac{c}{d}$. So with that fact, I did... $frac{a+b-c}{c}$=$frac{a-b+c}{b}$ $implies$
$frac{2a}{c+b}$ and $frac{2a}{c+b}$=$frac{-a+b+c}{a}$$implies$ $frac{(a+b+c)}{a+b+c}$ = 1. Then I took the original equations and did $frac{a+b-c}{c}$=1, so $a+b=2c$ , and similarly, $(a+c)=2b$ and $b+c=2a$. So plugging that into x=$frac{(a+b)(b+c)(c+a)}{abc}$ we have $x=frac{(2a)(2b)(2c)}{abc}$, which is $x=frac{8(abc)}{abc}=8$. This is wrong though, because it says in the problem x<0. So how do I do this?
algebra-precalculus fractions
$endgroup$
add a comment |
$begingroup$
I am getting stuck on this question:
If a, b, and c, are nonzero numbers such that $frac{a+b-c}{c}$=$frac{a-b+c}{b}$=$frac{-a+b+c}{a}$ and x=$frac{(a+b)(b+c)(c+a)}{abc}$ and x<0, then x=?
What I have done so far: Consider, if $frac{a}{b}$=$frac{c}{d}$, and (b+d) is non-zero, then $frac{a+c}{b+d}$=$frac{a}{b}$=$frac{c}{d}$. So with that fact, I did... $frac{a+b-c}{c}$=$frac{a-b+c}{b}$ $implies$
$frac{2a}{c+b}$ and $frac{2a}{c+b}$=$frac{-a+b+c}{a}$$implies$ $frac{(a+b+c)}{a+b+c}$ = 1. Then I took the original equations and did $frac{a+b-c}{c}$=1, so $a+b=2c$ , and similarly, $(a+c)=2b$ and $b+c=2a$. So plugging that into x=$frac{(a+b)(b+c)(c+a)}{abc}$ we have $x=frac{(2a)(2b)(2c)}{abc}$, which is $x=frac{8(abc)}{abc}=8$. This is wrong though, because it says in the problem x<0. So how do I do this?
algebra-precalculus fractions
$endgroup$
I am getting stuck on this question:
If a, b, and c, are nonzero numbers such that $frac{a+b-c}{c}$=$frac{a-b+c}{b}$=$frac{-a+b+c}{a}$ and x=$frac{(a+b)(b+c)(c+a)}{abc}$ and x<0, then x=?
What I have done so far: Consider, if $frac{a}{b}$=$frac{c}{d}$, and (b+d) is non-zero, then $frac{a+c}{b+d}$=$frac{a}{b}$=$frac{c}{d}$. So with that fact, I did... $frac{a+b-c}{c}$=$frac{a-b+c}{b}$ $implies$
$frac{2a}{c+b}$ and $frac{2a}{c+b}$=$frac{-a+b+c}{a}$$implies$ $frac{(a+b+c)}{a+b+c}$ = 1. Then I took the original equations and did $frac{a+b-c}{c}$=1, so $a+b=2c$ , and similarly, $(a+c)=2b$ and $b+c=2a$. So plugging that into x=$frac{(a+b)(b+c)(c+a)}{abc}$ we have $x=frac{(2a)(2b)(2c)}{abc}$, which is $x=frac{8(abc)}{abc}=8$. This is wrong though, because it says in the problem x<0. So how do I do this?
algebra-precalculus fractions
algebra-precalculus fractions
edited Dec 20 '18 at 17:49
Ankit Kumar
1,494221
1,494221
asked Dec 20 '18 at 17:26
Kenneth DangKenneth Dang
136
136
add a comment |
add a comment |
3 Answers
3
active
oldest
votes
$begingroup$
$$frac{a+b-c}{c}=frac{a-b+c}{b}$$
$$ab+b^2-bc=ac-bc+c^2implies a(b-c)=(b+c)(c-b)$$
$$implies b=c quad ORquad a+b+c=0$$
If we take $b=c$, $$frac{a}{c}=frac{-a+2c}{a}quad using (1)and (3).$$
$$implies ({frac{a}{c}})^2=1quad ORquad -2$$
Obviosuly $-2$ isn't possible, $a=c$ will give $x=1$ and $a=-c$ will give $x=0$.
So, $a+b+c=0implies a=-(b+c), b=-(a+c), c=-(a+b)implies x=-1.$
$endgroup$
1
$begingroup$
Dear Mr. Kumar, how do you know from a(b-c)=(b+c)(c-b) that b=c or a+b+c=0?
$endgroup$
– Kenneth Dang
Dec 20 '18 at 18:44
2
$begingroup$
$a(b-c)=(b+c)(c-b)$ is same as $a(b-c)+(b-c)(b+c)=0$ which is same as $(b-c)(a+b+c)=0$. Btw thank you, no one addressed me like that before ;)
$endgroup$
– Ankit Kumar
Dec 20 '18 at 18:49
add a comment |
$begingroup$
Hint: $$a=-frac{b}{2},b=b,c=-frac{b}{2}$$ solves your problem and $$x=-1$$
$endgroup$
add a comment |
$begingroup$
You correctly derived:
$$frac{2a}{c+b}=frac{-a+b+c}{a}$$
Your mistake is here:
Then I took the original equations and did $frac{a+b-c}{c}=1$
Instead, denote: $frac{b+c}{a}=t$, then the above equation becomes:
$$frac2{t}=-1+t Rightarrow t^2-t-2=0 Rightarrow t_1=-1 text{and} t_2=2.$$
Also note that:
$$frac{a+b-c}{c}=frac{a-b+c}{b}=frac{-a+b+c}{a}iff \
frac{a+b}{c}-1=frac{a+c}{b}-1=frac{b+c}{a}-1 iff \
frac{a+b}{c}=frac{a+c}{b}=frac{b+c}{a}=t.$$
Hence:
$$x=frac{(a+b)(b+c)(c+a)}{abc}=t^3=(-1)^3=-1;\
x=frac{(a+b)(b+c)(c+a)}{abc}=t^3=2^3not< 0.$$
$endgroup$
$begingroup$
Wow, I never thought of it like that. Do you an assertion as to when I should think similarly to this when dealing with problem solving?
$endgroup$
– Kenneth Dang
Dec 20 '18 at 20:59
add a comment |
Your Answer
StackExchange.ifUsing("editor", function () {
return StackExchange.using("mathjaxEditing", function () {
StackExchange.MarkdownEditor.creationCallbacks.add(function (editor, postfix) {
StackExchange.mathjaxEditing.prepareWmdForMathJax(editor, postfix, [["$", "$"], ["\\(","\\)"]]);
});
});
}, "mathjax-editing");
StackExchange.ready(function() {
var channelOptions = {
tags: "".split(" "),
id: "69"
};
initTagRenderer("".split(" "), "".split(" "), channelOptions);
StackExchange.using("externalEditor", function() {
// Have to fire editor after snippets, if snippets enabled
if (StackExchange.settings.snippets.snippetsEnabled) {
StackExchange.using("snippets", function() {
createEditor();
});
}
else {
createEditor();
}
});
function createEditor() {
StackExchange.prepareEditor({
heartbeatType: 'answer',
autoActivateHeartbeat: false,
convertImagesToLinks: true,
noModals: true,
showLowRepImageUploadWarning: true,
reputationToPostImages: 10,
bindNavPrevention: true,
postfix: "",
imageUploader: {
brandingHtml: "Powered by u003ca class="icon-imgur-white" href="https://imgur.com/"u003eu003c/au003e",
contentPolicyHtml: "User contributions licensed under u003ca href="https://creativecommons.org/licenses/by-sa/3.0/"u003ecc by-sa 3.0 with attribution requiredu003c/au003e u003ca href="https://stackoverflow.com/legal/content-policy"u003e(content policy)u003c/au003e",
allowUrls: true
},
noCode: true, onDemand: true,
discardSelector: ".discard-answer"
,immediatelyShowMarkdownHelp:true
});
}
});
Sign up or log in
StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
StackExchange.ready(
function () {
StackExchange.openid.initPostLogin('.new-post-login', 'https%3a%2f%2fmath.stackexchange.com%2fquestions%2f3047782%2famc-1834-if-a-b-and-c-are-nonzero-numbers-such-that-ab-c-c-a-bc-b%23new-answer', 'question_page');
}
);
Post as a guest
Required, but never shown
3 Answers
3
active
oldest
votes
3 Answers
3
active
oldest
votes
active
oldest
votes
active
oldest
votes
$begingroup$
$$frac{a+b-c}{c}=frac{a-b+c}{b}$$
$$ab+b^2-bc=ac-bc+c^2implies a(b-c)=(b+c)(c-b)$$
$$implies b=c quad ORquad a+b+c=0$$
If we take $b=c$, $$frac{a}{c}=frac{-a+2c}{a}quad using (1)and (3).$$
$$implies ({frac{a}{c}})^2=1quad ORquad -2$$
Obviosuly $-2$ isn't possible, $a=c$ will give $x=1$ and $a=-c$ will give $x=0$.
So, $a+b+c=0implies a=-(b+c), b=-(a+c), c=-(a+b)implies x=-1.$
$endgroup$
1
$begingroup$
Dear Mr. Kumar, how do you know from a(b-c)=(b+c)(c-b) that b=c or a+b+c=0?
$endgroup$
– Kenneth Dang
Dec 20 '18 at 18:44
2
$begingroup$
$a(b-c)=(b+c)(c-b)$ is same as $a(b-c)+(b-c)(b+c)=0$ which is same as $(b-c)(a+b+c)=0$. Btw thank you, no one addressed me like that before ;)
$endgroup$
– Ankit Kumar
Dec 20 '18 at 18:49
add a comment |
$begingroup$
$$frac{a+b-c}{c}=frac{a-b+c}{b}$$
$$ab+b^2-bc=ac-bc+c^2implies a(b-c)=(b+c)(c-b)$$
$$implies b=c quad ORquad a+b+c=0$$
If we take $b=c$, $$frac{a}{c}=frac{-a+2c}{a}quad using (1)and (3).$$
$$implies ({frac{a}{c}})^2=1quad ORquad -2$$
Obviosuly $-2$ isn't possible, $a=c$ will give $x=1$ and $a=-c$ will give $x=0$.
So, $a+b+c=0implies a=-(b+c), b=-(a+c), c=-(a+b)implies x=-1.$
$endgroup$
1
$begingroup$
Dear Mr. Kumar, how do you know from a(b-c)=(b+c)(c-b) that b=c or a+b+c=0?
$endgroup$
– Kenneth Dang
Dec 20 '18 at 18:44
2
$begingroup$
$a(b-c)=(b+c)(c-b)$ is same as $a(b-c)+(b-c)(b+c)=0$ which is same as $(b-c)(a+b+c)=0$. Btw thank you, no one addressed me like that before ;)
$endgroup$
– Ankit Kumar
Dec 20 '18 at 18:49
add a comment |
$begingroup$
$$frac{a+b-c}{c}=frac{a-b+c}{b}$$
$$ab+b^2-bc=ac-bc+c^2implies a(b-c)=(b+c)(c-b)$$
$$implies b=c quad ORquad a+b+c=0$$
If we take $b=c$, $$frac{a}{c}=frac{-a+2c}{a}quad using (1)and (3).$$
$$implies ({frac{a}{c}})^2=1quad ORquad -2$$
Obviosuly $-2$ isn't possible, $a=c$ will give $x=1$ and $a=-c$ will give $x=0$.
So, $a+b+c=0implies a=-(b+c), b=-(a+c), c=-(a+b)implies x=-1.$
$endgroup$
$$frac{a+b-c}{c}=frac{a-b+c}{b}$$
$$ab+b^2-bc=ac-bc+c^2implies a(b-c)=(b+c)(c-b)$$
$$implies b=c quad ORquad a+b+c=0$$
If we take $b=c$, $$frac{a}{c}=frac{-a+2c}{a}quad using (1)and (3).$$
$$implies ({frac{a}{c}})^2=1quad ORquad -2$$
Obviosuly $-2$ isn't possible, $a=c$ will give $x=1$ and $a=-c$ will give $x=0$.
So, $a+b+c=0implies a=-(b+c), b=-(a+c), c=-(a+b)implies x=-1.$
answered Dec 20 '18 at 17:43
Ankit KumarAnkit Kumar
1,494221
1,494221
1
$begingroup$
Dear Mr. Kumar, how do you know from a(b-c)=(b+c)(c-b) that b=c or a+b+c=0?
$endgroup$
– Kenneth Dang
Dec 20 '18 at 18:44
2
$begingroup$
$a(b-c)=(b+c)(c-b)$ is same as $a(b-c)+(b-c)(b+c)=0$ which is same as $(b-c)(a+b+c)=0$. Btw thank you, no one addressed me like that before ;)
$endgroup$
– Ankit Kumar
Dec 20 '18 at 18:49
add a comment |
1
$begingroup$
Dear Mr. Kumar, how do you know from a(b-c)=(b+c)(c-b) that b=c or a+b+c=0?
$endgroup$
– Kenneth Dang
Dec 20 '18 at 18:44
2
$begingroup$
$a(b-c)=(b+c)(c-b)$ is same as $a(b-c)+(b-c)(b+c)=0$ which is same as $(b-c)(a+b+c)=0$. Btw thank you, no one addressed me like that before ;)
$endgroup$
– Ankit Kumar
Dec 20 '18 at 18:49
1
1
$begingroup$
Dear Mr. Kumar, how do you know from a(b-c)=(b+c)(c-b) that b=c or a+b+c=0?
$endgroup$
– Kenneth Dang
Dec 20 '18 at 18:44
$begingroup$
Dear Mr. Kumar, how do you know from a(b-c)=(b+c)(c-b) that b=c or a+b+c=0?
$endgroup$
– Kenneth Dang
Dec 20 '18 at 18:44
2
2
$begingroup$
$a(b-c)=(b+c)(c-b)$ is same as $a(b-c)+(b-c)(b+c)=0$ which is same as $(b-c)(a+b+c)=0$. Btw thank you, no one addressed me like that before ;)
$endgroup$
– Ankit Kumar
Dec 20 '18 at 18:49
$begingroup$
$a(b-c)=(b+c)(c-b)$ is same as $a(b-c)+(b-c)(b+c)=0$ which is same as $(b-c)(a+b+c)=0$. Btw thank you, no one addressed me like that before ;)
$endgroup$
– Ankit Kumar
Dec 20 '18 at 18:49
add a comment |
$begingroup$
Hint: $$a=-frac{b}{2},b=b,c=-frac{b}{2}$$ solves your problem and $$x=-1$$
$endgroup$
add a comment |
$begingroup$
Hint: $$a=-frac{b}{2},b=b,c=-frac{b}{2}$$ solves your problem and $$x=-1$$
$endgroup$
add a comment |
$begingroup$
Hint: $$a=-frac{b}{2},b=b,c=-frac{b}{2}$$ solves your problem and $$x=-1$$
$endgroup$
Hint: $$a=-frac{b}{2},b=b,c=-frac{b}{2}$$ solves your problem and $$x=-1$$
answered Dec 20 '18 at 17:44
Dr. Sonnhard GraubnerDr. Sonnhard Graubner
76.5k42866
76.5k42866
add a comment |
add a comment |
$begingroup$
You correctly derived:
$$frac{2a}{c+b}=frac{-a+b+c}{a}$$
Your mistake is here:
Then I took the original equations and did $frac{a+b-c}{c}=1$
Instead, denote: $frac{b+c}{a}=t$, then the above equation becomes:
$$frac2{t}=-1+t Rightarrow t^2-t-2=0 Rightarrow t_1=-1 text{and} t_2=2.$$
Also note that:
$$frac{a+b-c}{c}=frac{a-b+c}{b}=frac{-a+b+c}{a}iff \
frac{a+b}{c}-1=frac{a+c}{b}-1=frac{b+c}{a}-1 iff \
frac{a+b}{c}=frac{a+c}{b}=frac{b+c}{a}=t.$$
Hence:
$$x=frac{(a+b)(b+c)(c+a)}{abc}=t^3=(-1)^3=-1;\
x=frac{(a+b)(b+c)(c+a)}{abc}=t^3=2^3not< 0.$$
$endgroup$
$begingroup$
Wow, I never thought of it like that. Do you an assertion as to when I should think similarly to this when dealing with problem solving?
$endgroup$
– Kenneth Dang
Dec 20 '18 at 20:59
add a comment |
$begingroup$
You correctly derived:
$$frac{2a}{c+b}=frac{-a+b+c}{a}$$
Your mistake is here:
Then I took the original equations and did $frac{a+b-c}{c}=1$
Instead, denote: $frac{b+c}{a}=t$, then the above equation becomes:
$$frac2{t}=-1+t Rightarrow t^2-t-2=0 Rightarrow t_1=-1 text{and} t_2=2.$$
Also note that:
$$frac{a+b-c}{c}=frac{a-b+c}{b}=frac{-a+b+c}{a}iff \
frac{a+b}{c}-1=frac{a+c}{b}-1=frac{b+c}{a}-1 iff \
frac{a+b}{c}=frac{a+c}{b}=frac{b+c}{a}=t.$$
Hence:
$$x=frac{(a+b)(b+c)(c+a)}{abc}=t^3=(-1)^3=-1;\
x=frac{(a+b)(b+c)(c+a)}{abc}=t^3=2^3not< 0.$$
$endgroup$
$begingroup$
Wow, I never thought of it like that. Do you an assertion as to when I should think similarly to this when dealing with problem solving?
$endgroup$
– Kenneth Dang
Dec 20 '18 at 20:59
add a comment |
$begingroup$
You correctly derived:
$$frac{2a}{c+b}=frac{-a+b+c}{a}$$
Your mistake is here:
Then I took the original equations and did $frac{a+b-c}{c}=1$
Instead, denote: $frac{b+c}{a}=t$, then the above equation becomes:
$$frac2{t}=-1+t Rightarrow t^2-t-2=0 Rightarrow t_1=-1 text{and} t_2=2.$$
Also note that:
$$frac{a+b-c}{c}=frac{a-b+c}{b}=frac{-a+b+c}{a}iff \
frac{a+b}{c}-1=frac{a+c}{b}-1=frac{b+c}{a}-1 iff \
frac{a+b}{c}=frac{a+c}{b}=frac{b+c}{a}=t.$$
Hence:
$$x=frac{(a+b)(b+c)(c+a)}{abc}=t^3=(-1)^3=-1;\
x=frac{(a+b)(b+c)(c+a)}{abc}=t^3=2^3not< 0.$$
$endgroup$
You correctly derived:
$$frac{2a}{c+b}=frac{-a+b+c}{a}$$
Your mistake is here:
Then I took the original equations and did $frac{a+b-c}{c}=1$
Instead, denote: $frac{b+c}{a}=t$, then the above equation becomes:
$$frac2{t}=-1+t Rightarrow t^2-t-2=0 Rightarrow t_1=-1 text{and} t_2=2.$$
Also note that:
$$frac{a+b-c}{c}=frac{a-b+c}{b}=frac{-a+b+c}{a}iff \
frac{a+b}{c}-1=frac{a+c}{b}-1=frac{b+c}{a}-1 iff \
frac{a+b}{c}=frac{a+c}{b}=frac{b+c}{a}=t.$$
Hence:
$$x=frac{(a+b)(b+c)(c+a)}{abc}=t^3=(-1)^3=-1;\
x=frac{(a+b)(b+c)(c+a)}{abc}=t^3=2^3not< 0.$$
answered Dec 20 '18 at 19:40
farruhotafarruhota
20.5k2739
20.5k2739
$begingroup$
Wow, I never thought of it like that. Do you an assertion as to when I should think similarly to this when dealing with problem solving?
$endgroup$
– Kenneth Dang
Dec 20 '18 at 20:59
add a comment |
$begingroup$
Wow, I never thought of it like that. Do you an assertion as to when I should think similarly to this when dealing with problem solving?
$endgroup$
– Kenneth Dang
Dec 20 '18 at 20:59
$begingroup$
Wow, I never thought of it like that. Do you an assertion as to when I should think similarly to this when dealing with problem solving?
$endgroup$
– Kenneth Dang
Dec 20 '18 at 20:59
$begingroup$
Wow, I never thought of it like that. Do you an assertion as to when I should think similarly to this when dealing with problem solving?
$endgroup$
– Kenneth Dang
Dec 20 '18 at 20:59
add a comment |
Thanks for contributing an answer to Mathematics Stack Exchange!
- Please be sure to answer the question. Provide details and share your research!
But avoid …
- Asking for help, clarification, or responding to other answers.
- Making statements based on opinion; back them up with references or personal experience.
Use MathJax to format equations. MathJax reference.
To learn more, see our tips on writing great answers.
Sign up or log in
StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
StackExchange.ready(
function () {
StackExchange.openid.initPostLogin('.new-post-login', 'https%3a%2f%2fmath.stackexchange.com%2fquestions%2f3047782%2famc-1834-if-a-b-and-c-are-nonzero-numbers-such-that-ab-c-c-a-bc-b%23new-answer', 'question_page');
}
);
Post as a guest
Required, but never shown
Sign up or log in
StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
Sign up or log in
StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
Sign up or log in
StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown