# Simplify symbolic expression in terms of constants [duplicate]

Say I have an expression $a+b+a\times b$ and I define $c:= a\times b$. How do I get Mathematica to write $a+b+a\times b$ in terms of $c$, i.e. $a+b+c$?

• Simplify[a + b + a*b, a == c/b] – Artes Sep 9 '13 at 13:38
• What about a + b + a b /. a b -> c ? – DavidC Sep 9 '13 at 13:50
• This is an oft-asked question with no simple answer. Really we need a canonical Q&A that addresses many variations in one place. Until that time here are some links to related questions. – Mr.Wizard Sep 9 '13 at 14:20