title: Excel Sigma Summation - Quadratic Expression
body: <p>I am trying to make a Variance summation in Excel. I know there is a function for it, but I want to use the Sigma summation:</p>
  
  <p><a href="https://i.stack.imgur.com/XHQSJ.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/XHQSJ.png" alt="enter image description here"></a></p>
  
  <p>I found some threads, but all of them assume a non-quadratic expression. This one for example: <a href="https://stackoverflow.com/questions/38044955/sigma-or-summation-function-in-excel/38045096">Sigma or Summation function in Excel</a></p>
  
  <p>I have the given data in Excel, and just need to put it together in this Sigma Summation. How would I write the function to make it work?</p>