cos/sin/tan function gives different result than my calculator : <p>If I enter </p>

<pre><code>cos(90)
</code></pre>

<p>I get</p>

<pre><code>-0.4480736
</code></pre>

<p>But my calculator gives</p>

<pre><code>0
</code></pre>

<p>I don't get it.</p>

<pre><code>?cos
 These functions give the obvious trigonometric functions.  They
 respectively compute the cosine, sine, tangent, arc-cosine,
 arc-sine, arc-tangent, and the two-argument arc-tangent.
</code></pre>

<p>Obvious?</p>
