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<A NAME=ACOS>

<TITLE>ACOS</TITLE></A>
<b><a href=r37_idx.html>INDEX</a></b><p><p>



<B>ACOS</B> _ _ _  _ _ _  _ _ _  _ _ _ <B>operator</B><P>
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The <em>acos</em> operator returns the arccosine of its argument. 
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 <P> <H3> 
syntax: </H3>
<em>acos</em>(&lt;expression&gt;) or <em>acos</em> &lt;simple\_expression&gt; 
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&lt;expression&gt; may be any scalar REDUCE expression, not an array, matrix or 

vector expression. &lt;simple\_expression&gt; must be a single identifier or 
begin with a prefix operator name. 
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 <P> <H3> 
examples: </H3>
<P><PRE><TT>
acos(ab); 

  ACOS(AB) 


acos 15; 

  ACOS(15) 


df(acos(x*y),x); 

           2  2
  SQRT( - X *Y  + 1)*Y
  -------------------- 
        2  2
       X *Y  - 1


on rounded; 

res := acos(sqrt(2)/2); 

  RES := 0.785398163397 


res-pi/4; 

  0

</TT></PRE><P>An explicit numeric value is not given unless the switch 
<A HREF=r37_0330.html>rounded</A> is 
on and the argument has an absolute numeric value less than or equal to 1. 
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