title: Correct way to calculate triangle area from 3 vertices
body: <p>Is this the correct way to calculate the area of a triangle given the 3 triangle points/vertices? The vertices will never be negative values.</p>
  
  <pre><code>def triangle_area(tri):
      x1, y1, x2, y2, x3, y3 = tri[0][0], tri[0][1], tri[1][0], tri[1][1], tri[2][0], tri[2][1]
      return 0.5 * (((x2-x1)*(y3-y1))-((x3-x1)*(y2-y1)))
  </code></pre>