questions about delayed expression.

*To*: mathgroup at smc.vnet.net*Subject*: [mg19862] questions about delayed expression.*From*: d8442803 at student.nsysu.edu.tw (Wen-Feng Hsiao)*Date*: Sun, 19 Sep 1999 01:20:45 -0400*Organization*: MIS*Sender*: owner-wri-mathgroup at wolfram.com

Hi, The following is the process that I run in my notebook. In[1]:= a[x_] := x + 4 b[x_] := -3 x + 8 In[2]:= sola = x /. Solve[{a[x] == c}, x]; solb = x /. Solve[{b[x] == c}, x]; In[3]:= Inter[c_] := Interval[{sola[[1]], solb[[1]]}] In[4]:= Inter[.3] Inter[.4] Out[4]= \!\(Interval[{\(-4\) + c, \(8 - c\)\/3}]\) Out[5]= \!\(Interval[{\(-4\) + c, \(8 - c\)\/3}]\) My questions are: 1. Why Inter[.3] and Inter[.4] cannot be evaluated? Their results should not be the same. This is not my intention. 2. I don't know if there is any better way to extract the 'root(s)' from the output of 'Solve' command. The output form is {{x->root1}, {x- >root2}, ...{}}. If I use 'ReplaceAll'(/.) command, it will remain a list of solutions of x. It seems I can only use element operation to extract the root(s) from the solution list? In my case, I use sola[[1]] and solb[[1]]. Please give me suggestions. Thanks for your help.

**Follow-Ups**:**Re: questions about delayed expression.***From:*"Wolf, Hartmut" <hwolf@debis.com>