title: Get right-hand side of equation
body: <p>I am calling the function <code>mnewton(0=expr, alpha, %pi/4)</code> to get the root of a rather complex equation <code>expr</code>. </p>
  
  <pre><code>%(i1)   mnewton(0=expr, alpha, %pi/4)
  %(o1)   [alpha=0.678193754078621]
  </code></pre>
  
  <p>I need to apply another function to this result (e.g. <code>sin</code>) and then want to plot it. Just linking the functions does not work:</p>
  
  <pre><code>%(i2)   sin(mnewton(0=expr, alpha, %pi/4)[1])
  %(o2)   sin(alpha=0.678193754078621)
  </code></pre>
  
  <p>This is because the expression <code>alpha=0.678193754078621</code> is not a number. <strong>How do I convert <code>alpha=0.678193754078621</code> to just <code>0.678193754078621</code>?</strong></p>
  
  <p>I can't just copy the numerical value and add it manually as I want to plot this and my <code>expr</code> will have a different root for each y.</p>