title: polyfit quadratic plot in python
body: <p>I am trying to plot a quadratic equation <code>y = a_0 + a_1*x + a_2*(x**2)</code> in python where points <code>(x,y)</code> are given. I have put the points into an array, but I'm having troubles with the plot. Can someone help me understand where I am going wrong with my code?</p>
  <pre class="lang-py prettyprint-override"><code>    data = np.array([[0,0],[1,1],[2,8],[3,8]])
      x = data[:,0]
      y = data[:,1]
      a_0, a_1, a_2 = np. polyfit(x, y,z, 1)
  </code></pre>
  <p>The last line returns error</p>
  <blockquote>
  <p>not enough values to          unpack (expected 3, got 2)</p>
  </blockquote>