How to expand $x^{1/3}-c^{1/3}$ into $(x-c)y$ for some $y$
$begingroup$
How to expand $x^{1/3}-c^{1/3}$ into $(x-c)y$ for some $y$
I know $x^3-c^3=(x-c)(x^2+xc+c^2)$ but I can't figure out how to pull this off with $1/3$ instead of $3$
factoring binomial-theorem
$endgroup$
add a comment |
$begingroup$
How to expand $x^{1/3}-c^{1/3}$ into $(x-c)y$ for some $y$
I know $x^3-c^3=(x-c)(x^2+xc+c^2)$ but I can't figure out how to pull this off with $1/3$ instead of $3$
factoring binomial-theorem
$endgroup$
$begingroup$
I don't think any similar rule applies for non-integers powers in terms of factorising polynomials
$endgroup$
– Henry Lee
Dec 5 '18 at 1:13
$begingroup$
Technically speaking that isn't "expanding" so much as factoring.
$endgroup$
– fleablood
Dec 5 '18 at 1:28
1
$begingroup$
"I don't think any similar rule applies for non-integers powers in terms of factorising polynomials" Sure there are. Just take $sqrt[k] x = M$ and $x = M^k$ anc $sqrt[k]c = N$. Then $x -c = (M^k - N^k)(M^{k-1}+ ... N^{k-1})= (sqrt[k] x - sqrt[k] c)(sqrt[k] x^{k-1} +.... + sqrt[k]c^{k-1})$
$endgroup$
– fleablood
Dec 5 '18 at 1:32
add a comment |
$begingroup$
How to expand $x^{1/3}-c^{1/3}$ into $(x-c)y$ for some $y$
I know $x^3-c^3=(x-c)(x^2+xc+c^2)$ but I can't figure out how to pull this off with $1/3$ instead of $3$
factoring binomial-theorem
$endgroup$
How to expand $x^{1/3}-c^{1/3}$ into $(x-c)y$ for some $y$
I know $x^3-c^3=(x-c)(x^2+xc+c^2)$ but I can't figure out how to pull this off with $1/3$ instead of $3$
factoring binomial-theorem
factoring binomial-theorem
edited Dec 5 '18 at 15:05
Did
247k23222458
247k23222458
asked Dec 5 '18 at 1:11
Albert DiazAlbert Diaz
925
925
$begingroup$
I don't think any similar rule applies for non-integers powers in terms of factorising polynomials
$endgroup$
– Henry Lee
Dec 5 '18 at 1:13
$begingroup$
Technically speaking that isn't "expanding" so much as factoring.
$endgroup$
– fleablood
Dec 5 '18 at 1:28
1
$begingroup$
"I don't think any similar rule applies for non-integers powers in terms of factorising polynomials" Sure there are. Just take $sqrt[k] x = M$ and $x = M^k$ anc $sqrt[k]c = N$. Then $x -c = (M^k - N^k)(M^{k-1}+ ... N^{k-1})= (sqrt[k] x - sqrt[k] c)(sqrt[k] x^{k-1} +.... + sqrt[k]c^{k-1})$
$endgroup$
– fleablood
Dec 5 '18 at 1:32
add a comment |
$begingroup$
I don't think any similar rule applies for non-integers powers in terms of factorising polynomials
$endgroup$
– Henry Lee
Dec 5 '18 at 1:13
$begingroup$
Technically speaking that isn't "expanding" so much as factoring.
$endgroup$
– fleablood
Dec 5 '18 at 1:28
1
$begingroup$
"I don't think any similar rule applies for non-integers powers in terms of factorising polynomials" Sure there are. Just take $sqrt[k] x = M$ and $x = M^k$ anc $sqrt[k]c = N$. Then $x -c = (M^k - N^k)(M^{k-1}+ ... N^{k-1})= (sqrt[k] x - sqrt[k] c)(sqrt[k] x^{k-1} +.... + sqrt[k]c^{k-1})$
$endgroup$
– fleablood
Dec 5 '18 at 1:32
$begingroup$
I don't think any similar rule applies for non-integers powers in terms of factorising polynomials
$endgroup$
– Henry Lee
Dec 5 '18 at 1:13
$begingroup$
I don't think any similar rule applies for non-integers powers in terms of factorising polynomials
$endgroup$
– Henry Lee
Dec 5 '18 at 1:13
$begingroup$
Technically speaking that isn't "expanding" so much as factoring.
$endgroup$
– fleablood
Dec 5 '18 at 1:28
$begingroup$
Technically speaking that isn't "expanding" so much as factoring.
$endgroup$
– fleablood
Dec 5 '18 at 1:28
1
1
$begingroup$
"I don't think any similar rule applies for non-integers powers in terms of factorising polynomials" Sure there are. Just take $sqrt[k] x = M$ and $x = M^k$ anc $sqrt[k]c = N$. Then $x -c = (M^k - N^k)(M^{k-1}+ ... N^{k-1})= (sqrt[k] x - sqrt[k] c)(sqrt[k] x^{k-1} +.... + sqrt[k]c^{k-1})$
$endgroup$
– fleablood
Dec 5 '18 at 1:32
$begingroup$
"I don't think any similar rule applies for non-integers powers in terms of factorising polynomials" Sure there are. Just take $sqrt[k] x = M$ and $x = M^k$ anc $sqrt[k]c = N$. Then $x -c = (M^k - N^k)(M^{k-1}+ ... N^{k-1})= (sqrt[k] x - sqrt[k] c)(sqrt[k] x^{k-1} +.... + sqrt[k]c^{k-1})$
$endgroup$
– fleablood
Dec 5 '18 at 1:32
add a comment |
3 Answers
3
active
oldest
votes
$begingroup$
Replace $x$ with $(x^{frac 13})^3$ and $c = (c^{frac 13})^3$ and so
$x - c = (x^{frac 13})^3 - (c^{frac 13})^3 = (x^{frac 13} - c^{frac 13})((x^{frac 13})^2 + x^{frac 13}y^{frac 13} + (c^{frac 13})^2)$
So
$(x -c) frac 1{x^{frac 23} + x^{frac 13}y^{frac 13} + c^{frac 23}}= x^{frac 13}- c^{frac 13}$
So $y = frac 1{x^{frac 23} + x^{frac 13}y^{frac 13} + c^{frac 23}}$
There IS the assumption that $x^{frac 23} + x^{frac 13}y^{frac 13} + c^{frac 23} ne 0$. But if $x^{frac 23} + x^{frac 13}y^{frac 13} + c^{frac 23} = 0$ then $x - c = (x^{frac 13})^3 - (c^{frac 13})^3 = (x^{frac 13} - c^{frac 13})((x^{frac 13})^2 + x^{frac 13}y^{frac 13} + (c^{frac 13})^2) = 0$ and $x = c$ and $x^{frac 13} = c^{frac 13}$ and $y$ could be anything.
$endgroup$
add a comment |
$begingroup$
Yes your way is right, let use that
$$A^3-B^3=(A-B)(A^2+AB+B^2)$$
with $A^3=x$ and $B^3=c$.
Then
$$x^{1/3}-c^{1/3}=(x-c)cdot frac1{x^{2/3}+x^{1/3}c^{1/3}+c^{2/3}}$$
$endgroup$
add a comment |
$begingroup$
Write $w=x-c$. You want to expand in powers of $w$. So, as $w to 0$ we have
begin{align}
x^{1/3} &= (c+w)^{1/3} = c^{1/3}left(1+frac{w}{c}right)^{1/3}
\
&= c^{1/3}left(1+frac{w}{3c}-frac{w^2}{9c^2}+frac{5w^3}{81c^3}+dotsright)
\
&= c^{1/3}+frac{w}{3c^{2/3}}-frac{w^2}{9c^{5/3}}+frac{5w^3}{81c^{8/3}}+dots
\
x^{1/3} - c^{1/3} &= frac{w}{3c^{2/3}}-frac{w^2}{9c^{5/3}}+frac{5w^3}{81c^{8/3}}+dots
\
&= wleft(frac{1}{3c^{2/3}}-frac{w}{9c^{5/3}}+frac{5w^2}{81c^{8/3}}+dotsright)
\
&= (x-c)left(frac{1}{3c^{2/3}}-frac{x-c}{9c^{5/3}}+frac{5(x-c)^2}{81c^{8/3}}+dotsright)
end{align}
Of course the last factor is exactly
$$
frac{x^{1/3}-c^{1/3}}{x-c} ,
$$
which is an analytic function (removable singularity) near $x=c$.
$endgroup$
1
$begingroup$
Good God! Really?
$endgroup$
– fleablood
Dec 5 '18 at 1:34
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%2f3026458%2fhow-to-expand-x1-3-c1-3-into-x-cy-for-some-y%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
$begingroup$
Replace $x$ with $(x^{frac 13})^3$ and $c = (c^{frac 13})^3$ and so
$x - c = (x^{frac 13})^3 - (c^{frac 13})^3 = (x^{frac 13} - c^{frac 13})((x^{frac 13})^2 + x^{frac 13}y^{frac 13} + (c^{frac 13})^2)$
So
$(x -c) frac 1{x^{frac 23} + x^{frac 13}y^{frac 13} + c^{frac 23}}= x^{frac 13}- c^{frac 13}$
So $y = frac 1{x^{frac 23} + x^{frac 13}y^{frac 13} + c^{frac 23}}$
There IS the assumption that $x^{frac 23} + x^{frac 13}y^{frac 13} + c^{frac 23} ne 0$. But if $x^{frac 23} + x^{frac 13}y^{frac 13} + c^{frac 23} = 0$ then $x - c = (x^{frac 13})^3 - (c^{frac 13})^3 = (x^{frac 13} - c^{frac 13})((x^{frac 13})^2 + x^{frac 13}y^{frac 13} + (c^{frac 13})^2) = 0$ and $x = c$ and $x^{frac 13} = c^{frac 13}$ and $y$ could be anything.
$endgroup$
add a comment |
$begingroup$
Replace $x$ with $(x^{frac 13})^3$ and $c = (c^{frac 13})^3$ and so
$x - c = (x^{frac 13})^3 - (c^{frac 13})^3 = (x^{frac 13} - c^{frac 13})((x^{frac 13})^2 + x^{frac 13}y^{frac 13} + (c^{frac 13})^2)$
So
$(x -c) frac 1{x^{frac 23} + x^{frac 13}y^{frac 13} + c^{frac 23}}= x^{frac 13}- c^{frac 13}$
So $y = frac 1{x^{frac 23} + x^{frac 13}y^{frac 13} + c^{frac 23}}$
There IS the assumption that $x^{frac 23} + x^{frac 13}y^{frac 13} + c^{frac 23} ne 0$. But if $x^{frac 23} + x^{frac 13}y^{frac 13} + c^{frac 23} = 0$ then $x - c = (x^{frac 13})^3 - (c^{frac 13})^3 = (x^{frac 13} - c^{frac 13})((x^{frac 13})^2 + x^{frac 13}y^{frac 13} + (c^{frac 13})^2) = 0$ and $x = c$ and $x^{frac 13} = c^{frac 13}$ and $y$ could be anything.
$endgroup$
add a comment |
$begingroup$
Replace $x$ with $(x^{frac 13})^3$ and $c = (c^{frac 13})^3$ and so
$x - c = (x^{frac 13})^3 - (c^{frac 13})^3 = (x^{frac 13} - c^{frac 13})((x^{frac 13})^2 + x^{frac 13}y^{frac 13} + (c^{frac 13})^2)$
So
$(x -c) frac 1{x^{frac 23} + x^{frac 13}y^{frac 13} + c^{frac 23}}= x^{frac 13}- c^{frac 13}$
So $y = frac 1{x^{frac 23} + x^{frac 13}y^{frac 13} + c^{frac 23}}$
There IS the assumption that $x^{frac 23} + x^{frac 13}y^{frac 13} + c^{frac 23} ne 0$. But if $x^{frac 23} + x^{frac 13}y^{frac 13} + c^{frac 23} = 0$ then $x - c = (x^{frac 13})^3 - (c^{frac 13})^3 = (x^{frac 13} - c^{frac 13})((x^{frac 13})^2 + x^{frac 13}y^{frac 13} + (c^{frac 13})^2) = 0$ and $x = c$ and $x^{frac 13} = c^{frac 13}$ and $y$ could be anything.
$endgroup$
Replace $x$ with $(x^{frac 13})^3$ and $c = (c^{frac 13})^3$ and so
$x - c = (x^{frac 13})^3 - (c^{frac 13})^3 = (x^{frac 13} - c^{frac 13})((x^{frac 13})^2 + x^{frac 13}y^{frac 13} + (c^{frac 13})^2)$
So
$(x -c) frac 1{x^{frac 23} + x^{frac 13}y^{frac 13} + c^{frac 23}}= x^{frac 13}- c^{frac 13}$
So $y = frac 1{x^{frac 23} + x^{frac 13}y^{frac 13} + c^{frac 23}}$
There IS the assumption that $x^{frac 23} + x^{frac 13}y^{frac 13} + c^{frac 23} ne 0$. But if $x^{frac 23} + x^{frac 13}y^{frac 13} + c^{frac 23} = 0$ then $x - c = (x^{frac 13})^3 - (c^{frac 13})^3 = (x^{frac 13} - c^{frac 13})((x^{frac 13})^2 + x^{frac 13}y^{frac 13} + (c^{frac 13})^2) = 0$ and $x = c$ and $x^{frac 13} = c^{frac 13}$ and $y$ could be anything.
answered Dec 5 '18 at 1:24
fleabloodfleablood
69.3k22685
69.3k22685
add a comment |
add a comment |
$begingroup$
Yes your way is right, let use that
$$A^3-B^3=(A-B)(A^2+AB+B^2)$$
with $A^3=x$ and $B^3=c$.
Then
$$x^{1/3}-c^{1/3}=(x-c)cdot frac1{x^{2/3}+x^{1/3}c^{1/3}+c^{2/3}}$$
$endgroup$
add a comment |
$begingroup$
Yes your way is right, let use that
$$A^3-B^3=(A-B)(A^2+AB+B^2)$$
with $A^3=x$ and $B^3=c$.
Then
$$x^{1/3}-c^{1/3}=(x-c)cdot frac1{x^{2/3}+x^{1/3}c^{1/3}+c^{2/3}}$$
$endgroup$
add a comment |
$begingroup$
Yes your way is right, let use that
$$A^3-B^3=(A-B)(A^2+AB+B^2)$$
with $A^3=x$ and $B^3=c$.
Then
$$x^{1/3}-c^{1/3}=(x-c)cdot frac1{x^{2/3}+x^{1/3}c^{1/3}+c^{2/3}}$$
$endgroup$
Yes your way is right, let use that
$$A^3-B^3=(A-B)(A^2+AB+B^2)$$
with $A^3=x$ and $B^3=c$.
Then
$$x^{1/3}-c^{1/3}=(x-c)cdot frac1{x^{2/3}+x^{1/3}c^{1/3}+c^{2/3}}$$
edited Dec 5 '18 at 1:29
answered Dec 5 '18 at 1:18
gimusigimusi
92.8k94494
92.8k94494
add a comment |
add a comment |
$begingroup$
Write $w=x-c$. You want to expand in powers of $w$. So, as $w to 0$ we have
begin{align}
x^{1/3} &= (c+w)^{1/3} = c^{1/3}left(1+frac{w}{c}right)^{1/3}
\
&= c^{1/3}left(1+frac{w}{3c}-frac{w^2}{9c^2}+frac{5w^3}{81c^3}+dotsright)
\
&= c^{1/3}+frac{w}{3c^{2/3}}-frac{w^2}{9c^{5/3}}+frac{5w^3}{81c^{8/3}}+dots
\
x^{1/3} - c^{1/3} &= frac{w}{3c^{2/3}}-frac{w^2}{9c^{5/3}}+frac{5w^3}{81c^{8/3}}+dots
\
&= wleft(frac{1}{3c^{2/3}}-frac{w}{9c^{5/3}}+frac{5w^2}{81c^{8/3}}+dotsright)
\
&= (x-c)left(frac{1}{3c^{2/3}}-frac{x-c}{9c^{5/3}}+frac{5(x-c)^2}{81c^{8/3}}+dotsright)
end{align}
Of course the last factor is exactly
$$
frac{x^{1/3}-c^{1/3}}{x-c} ,
$$
which is an analytic function (removable singularity) near $x=c$.
$endgroup$
1
$begingroup$
Good God! Really?
$endgroup$
– fleablood
Dec 5 '18 at 1:34
add a comment |
$begingroup$
Write $w=x-c$. You want to expand in powers of $w$. So, as $w to 0$ we have
begin{align}
x^{1/3} &= (c+w)^{1/3} = c^{1/3}left(1+frac{w}{c}right)^{1/3}
\
&= c^{1/3}left(1+frac{w}{3c}-frac{w^2}{9c^2}+frac{5w^3}{81c^3}+dotsright)
\
&= c^{1/3}+frac{w}{3c^{2/3}}-frac{w^2}{9c^{5/3}}+frac{5w^3}{81c^{8/3}}+dots
\
x^{1/3} - c^{1/3} &= frac{w}{3c^{2/3}}-frac{w^2}{9c^{5/3}}+frac{5w^3}{81c^{8/3}}+dots
\
&= wleft(frac{1}{3c^{2/3}}-frac{w}{9c^{5/3}}+frac{5w^2}{81c^{8/3}}+dotsright)
\
&= (x-c)left(frac{1}{3c^{2/3}}-frac{x-c}{9c^{5/3}}+frac{5(x-c)^2}{81c^{8/3}}+dotsright)
end{align}
Of course the last factor is exactly
$$
frac{x^{1/3}-c^{1/3}}{x-c} ,
$$
which is an analytic function (removable singularity) near $x=c$.
$endgroup$
1
$begingroup$
Good God! Really?
$endgroup$
– fleablood
Dec 5 '18 at 1:34
add a comment |
$begingroup$
Write $w=x-c$. You want to expand in powers of $w$. So, as $w to 0$ we have
begin{align}
x^{1/3} &= (c+w)^{1/3} = c^{1/3}left(1+frac{w}{c}right)^{1/3}
\
&= c^{1/3}left(1+frac{w}{3c}-frac{w^2}{9c^2}+frac{5w^3}{81c^3}+dotsright)
\
&= c^{1/3}+frac{w}{3c^{2/3}}-frac{w^2}{9c^{5/3}}+frac{5w^3}{81c^{8/3}}+dots
\
x^{1/3} - c^{1/3} &= frac{w}{3c^{2/3}}-frac{w^2}{9c^{5/3}}+frac{5w^3}{81c^{8/3}}+dots
\
&= wleft(frac{1}{3c^{2/3}}-frac{w}{9c^{5/3}}+frac{5w^2}{81c^{8/3}}+dotsright)
\
&= (x-c)left(frac{1}{3c^{2/3}}-frac{x-c}{9c^{5/3}}+frac{5(x-c)^2}{81c^{8/3}}+dotsright)
end{align}
Of course the last factor is exactly
$$
frac{x^{1/3}-c^{1/3}}{x-c} ,
$$
which is an analytic function (removable singularity) near $x=c$.
$endgroup$
Write $w=x-c$. You want to expand in powers of $w$. So, as $w to 0$ we have
begin{align}
x^{1/3} &= (c+w)^{1/3} = c^{1/3}left(1+frac{w}{c}right)^{1/3}
\
&= c^{1/3}left(1+frac{w}{3c}-frac{w^2}{9c^2}+frac{5w^3}{81c^3}+dotsright)
\
&= c^{1/3}+frac{w}{3c^{2/3}}-frac{w^2}{9c^{5/3}}+frac{5w^3}{81c^{8/3}}+dots
\
x^{1/3} - c^{1/3} &= frac{w}{3c^{2/3}}-frac{w^2}{9c^{5/3}}+frac{5w^3}{81c^{8/3}}+dots
\
&= wleft(frac{1}{3c^{2/3}}-frac{w}{9c^{5/3}}+frac{5w^2}{81c^{8/3}}+dotsright)
\
&= (x-c)left(frac{1}{3c^{2/3}}-frac{x-c}{9c^{5/3}}+frac{5(x-c)^2}{81c^{8/3}}+dotsright)
end{align}
Of course the last factor is exactly
$$
frac{x^{1/3}-c^{1/3}}{x-c} ,
$$
which is an analytic function (removable singularity) near $x=c$.
edited Dec 5 '18 at 1:38
answered Dec 5 '18 at 1:28
GEdgarGEdgar
62.2k267168
62.2k267168
1
$begingroup$
Good God! Really?
$endgroup$
– fleablood
Dec 5 '18 at 1:34
add a comment |
1
$begingroup$
Good God! Really?
$endgroup$
– fleablood
Dec 5 '18 at 1:34
1
1
$begingroup$
Good God! Really?
$endgroup$
– fleablood
Dec 5 '18 at 1:34
$begingroup$
Good God! Really?
$endgroup$
– fleablood
Dec 5 '18 at 1:34
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%2f3026458%2fhow-to-expand-x1-3-c1-3-into-x-cy-for-some-y%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
$begingroup$
I don't think any similar rule applies for non-integers powers in terms of factorising polynomials
$endgroup$
– Henry Lee
Dec 5 '18 at 1:13
$begingroup$
Technically speaking that isn't "expanding" so much as factoring.
$endgroup$
– fleablood
Dec 5 '18 at 1:28
1
$begingroup$
"I don't think any similar rule applies for non-integers powers in terms of factorising polynomials" Sure there are. Just take $sqrt[k] x = M$ and $x = M^k$ anc $sqrt[k]c = N$. Then $x -c = (M^k - N^k)(M^{k-1}+ ... N^{k-1})= (sqrt[k] x - sqrt[k] c)(sqrt[k] x^{k-1} +.... + sqrt[k]c^{k-1})$
$endgroup$
– fleablood
Dec 5 '18 at 1:32