• 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]].