title: How to calculate the derivate of a function for a set variable?
body: <p>Let's say I input following sentences:</p>
  
  <pre><code>x = 5
  y = x.^2
  z = diff(y)
  </code></pre>
  
  <p>But I'll be getting</p>
  
  <pre><code>z =
  
       []
  </code></pre>
  
  <p>as result, while I'd like to get the actual value of <code>2x</code> as result, that is <code>10</code>.</p>
  
  <p>I know the existance of <code>syms</code> and I've tried adding it for <code>x</code> and <code>y</code> values but got not results.</p>