3
$\begingroup$
f1 = a x^2 + b x + c + x^3

(* a x^2+b x+c+x^3 *)

f1 /. x -> (x - a/3) // Expand

(* (2 a^3)/27-(a^2 x)/3-(a b)/3+b x+c+x^3 *)

I've tried this:

f1 /. x -> (x - a/3) // Expand // Collect[#, x] &

(* (2 a^3)/27+x (b-a^2/3)-(a b)/3+c+x^3 *)

f1 /. x -> (x - a/3) // Expand // Collect[#, x] & // PolynomialForm

(* (2 a^3)/27-(b a)/3+x^3+c+(b-a^2/3) x *)

$\endgroup$
1
  • 1
    $\begingroup$ You can extract the coefficients of $x$ as a list using f1 /. x -> (x - a/3) // CoefficientList[#, x] &. $\endgroup$ Nov 19 '13 at 17:36
6
$\begingroup$

Try this formatting

OrderedForm[x_] := HoldForm[+##] & @@ (x^#1[[1]] #2 & @@@ CoefficientRules[#, x]) &;

f1 /. x -> (x - a/3) // OrderedForm[x]
x^3+(-(a^2/3)+b) x+((2 a^3)/27-(a b)/3+c)

See also my answer here.

$\endgroup$
1
$\begingroup$

The OP almost had it with attempting to use PolynomialForm[]. All that was missing is the use of an appropriate setting:

PolynomialForm[a x^2 + b x + c + x^3 /. x -> (x - a/3), 
               TraditionalOrder -> True]
   (x - a/3)^3 + a (x - a/3)^2 + b (x - a/3) + c

As is usual with *Form[] functions, this is only suitable for display/pretty printing.

$\endgroup$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.