ArcCos[]

• To: mathgroup at smc.vnet.net
• Subject: [mg24730] ArcCos[]
• From: Gianluca Gorni <gorni at dimi.uniud.it>
• Date: Wed, 9 Aug 2000 02:31:30 -0400 (EDT)
• Sender: owner-wri-mathgroup at wolfram.com

```Hello!

I have just come across one more example that shows how there is
room for improving Mathematica's trig functions.

With Mathematica 4:

v = Cos[ Pi/8 ] // FunctionExpand   gives   Sqrt[2 + Sqrt[2]]/2

Still, neither

ArcCos[v] // FunctionExpand   nor    ArcCos[v] // FullSimplify

give  Pi/8, as I would expect, but just

ArcSec[2/Sqrt[2 + Sqrt[2]]]

%%%%%%%%%%%%%%%

An unrelated problem: the following instructions consistently crash
my Mac Mathematica 4 kernel:

a = Root[-t + 2*#1 + 2*t^2*#1 + #1^3 & , 1];
b = D[a, t];
Solve[b == 0, t]

%%%%%%%%%%%%%%%

Best regards,

Gianluca Gorni

--

+---------------------------------+
| Gianluca Gorni                  |
| Universita` di Udine            |
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| via delle Scienze 208           |
| I-33100 Udine UD                |
| Italy                           |
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| mailto:gorni at dimi.uniud.it      |
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+---------------------------------+

```

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