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<a name="acos_002c-acosf_002d_002d_002darc-cosine"></a>
<h3 class="section">1.3 <code>acos</code>, <code>acosf</code>&mdash;arc cosine</h3>
<a name="index-acos"></a>
<a name="index-acosf"></a>
<p><strong>Synopsis</strong>
</p><div class="example">
<pre class="example">#include &lt;math.h&gt;
double acos(double <var>x</var>);
float acosf(float <var>x</var>);

</pre></div>
<p><strong>Description</strong><br>
</p>
<p><code>acos</code> computes the inverse cosine (arc cosine) of the input value.
Arguments to <code>acos</code> must be in the range -1 to 1. 
</p>
<p><code>acosf</code> is identical to <code>acos</code>, except that it performs
its calculations on <code>floats</code>.
</p>
<br>
<p><strong>Returns</strong><br>
<code>acos</code> and <code>acosf</code> return values in radians, in the range of 0 to pi.
</p>
<p>If <var>x</var> is not between -1 and 1, the returned value is NaN
(not a number), and the global variable <code>errno</code> is set to <code>EDOM</code>.
</p>
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