I finally got your full question as you posted it to my email address. I am happy that you worked the example through. The note on that page was truncated at a point because the equation was too long. I have included the full equation in my reply as you can read below.
The error in your effort is at term 4 as I have changed its colour to red for emphasis. In my reply, I have also painted the result that leads to that value red for you to look again and compare. It is likely that by so doing, you will be able to see your mistake. Here is the full text of your question with my response.
I sure hope this helps.