Can someone explain why Mathematica is doing this?

• To: mathgroup at smc.vnet.net
• Subject: [mg19113] Can someone explain why Mathematica is doing this?
• From: belotto at vassar.edu (Benjamin Lotto)
• Date: Thu, 5 Aug 1999 01:35:30 -0400
• Organization: Vassar College
• Sender: owner-wri-mathgroup at wolfram.com

```I'm running Mathematica v3.0.1.1x (or something like that) on a Macintosh.  I want
to replace Tan[something] with Sin[something]/Cos[something].  The obvious
substitution (see below) didn't work.  Other substitutions work fine, but
this one just sits there.  Perhaps (it has just occured to me) Mathematica is
making the substitution, but then "simplifying" Sin/Cos->Tan.  However, I
want to make other substitutions (to check some algebra that I'm doing by
hand).  How can I make Mathematica do this?

-Ben

In[6]:=Tan[x]/.Tan[z_]->Sin[z]

Out[6]=Sin[x]

In[7]:=Tan[x]/.Tan[z_]->z Sin[z]

Out[7]=x Sin[x]

In[8]:=Tan[x]/.Tan[z_]->Sin[z]Cos[z]

Out[8]=Cos[x] Sin[x]

In[9]:=Tan[x]/.Tan[z_]->Sin[z]/Cos[z]

Out[9]=Tan[x]

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```

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