Re: How to use the result of Solve in Plot?

*To*: mathgroup at smc.vnet.net*Subject*: [mg111653] Re: How to use the result of Solve in Plot?*From*: Bill Rowe <readnews at sbcglobal.net>*Date*: Mon, 9 Aug 2010 05:13:07 -0400 (EDT)

On 8/8/10 at 7:20 AM, emammendes at gmail.com (Eduardo M. A. M.Mendes) wrote: >I want to use the result of Solve[{5*x+4*y==12},{y}] in >Plot[.,{x,0,2}]. Plot[Solve[.],{x,0,2}] does not work. Solve returns results as a list of replacement rules. So, what you need to do is: sol = Solve[{5*x + 4*y == 12}, {y}]; Plot[y /. First[sol], {x, 0, 5}] Note, the use of First. Since Solve is intended to solve for more than one variable and provide all possible solutions the result is a nested list rather than a flat list. In this particular case where there is only one variable and only one solution Plot[y/.sol, {x, 0, 5}] will create the same plot. But in general, you will need to select one of the solutions using something like First. So, it is a good idea to not get into the habit of thinking Plot[y/.sol ... will always work.