I will explain my problem with an example.
I have : $Cj=j(j+1)$ and $dj=(2*j+1)$
In mathematica I have a variable "a" that is equal to : $j(j+1)(2*j+1)$
How can I tell him to recognize that $a$ is in fact equal to $Cj*dj$. So I want him to write $Cj*dj$ instead of $j(j+1)(2*j+1)$.
In fact, each time he "see" a term $j(j+1)$, he will understand that he has to replace it by $cj$ (and same for $dj$).
I did the following :
In[3]:= Solve[ppp == J (1 + J) && x = J (J + 1), {ppp}, {x}]
But mathematica answers me :
Set::write: Tag And in ppp==J (1+J)&&x is Protected.
Solve::naqs: \!\(\*SubscriptBox[\(\[Exists]\), \({x}\)]\(J\ \((1 + J)\)\)\) is not a quantified system of equations and inequalities.
I saw this method from here :
How do I replace a variable in a polynomial?
Why it doesn't work and how to do it ?
=vs==). – Ruslan Jun 14 '17 at 15:41