solve hangs on Arc Functions

• To: mathgroup at yoda.ncsa.uiuc.edu (mathgroup for mathematica)
• Subject: solve hangs on Arc Functions
• From: Steven Warwick <sdw at hpsadsdw.hp.com>
• Date: Wed, 5 Sep 90 9:11:48 PDT

```There appears to be a bug in solve in which expressions
involving Arc Trig functions cause Mma to hang with no return...

***************** This hangs

In[3]:= ww==ArcCos[ (4-ts^2 wc^2)/ (4+ts^2 wc^2)]

2   2
4 - ts  wc
Out[3]= ww == ArcCos[-----------]
2   2
4 + ts  wc

In[4]:= Solve[%,wc]

***********  this doesn't **********

In[4]:=  Cos[wt] == (4-ts^2 wc^2)/ (4+ts^2 wc^2)

2   2
4 - ts  wc
Out[4]= Cos[wt] == -----------
2   2
4 + ts  wc

In[5]:= Solve[%,wc]

Sqrt[4 - 4 Cos[wt]]                Sqrt[4 - 4 Cos[wt]]
Out[5]= {{wc -> -----------------------}, {wc -> -(-----------------------)}}
2     2                            2     2
Sqrt[ts  + ts  Cos[wt]]            Sqrt[ts  + ts  Cos[wt]]

**********************************

Watch out.....

--
Steven Warwick

Hewlett-Packard