Mathematica Stack Exchange is a question and answer site for users of Mathematica. It's 100% free, no registration required.

Sign up
Here's how it works:
  1. Anybody can ask a question
  2. Anybody can answer
  3. The best answers are voted up and rise to the top

This question already has an answer here:

I have an equation that defines a variable like y=4x+a. I had another equation, z=x+2+4, I would like to know if there is a way in Mathematica to get an expression in which z= a*y+C, in which a and C are combinations of constants. These equations are examples, the equations I working are more complicated... (thanks for the patience I am newbie here)

share|improve this question

marked as duplicate by Mr.Wizard Jan 11 '14 at 4:01

This question was marked as an exact duplicate of an existing question.

If my approach doesn't work, it would help for you to provide the full equation that you're working with, so that the community can think of specific tricks that we can implement. – Vincent Tjeng Jan 11 '14 at 3:51
I am marking this question as a duplicate, because I believe it has been asked multiple times before in slightly different forms. Please see my answer in the duplicate for extensive links. If after reviewing these you feel your question is not a duplicate let me know in these comments. – Mr.Wizard Jan 11 '14 at 4:01

Depending on the complexity of the equations you are working with, the following method might work.

(z == x + 2 + 4) /. Solve[y == 4 x + a, x]

(* output is {z == 6 + 1/4 (-a + y)} *)

What this does is to solve the first equation for x, and substitute this value in the original equation.

share|improve this answer

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