Defining Riemann sums using summation notation causes incorrect index for the first two terms of the sum

Something’s not working the way it seems like it should.

When I was using Desmos to create an activity for integration, accumulation functions, and partial sums…

I saw that the first two terms of the sum were incorrect (the summation appeared to be pulling the first two terms using k = 1 and k = 1 instead of k = 1 and k = 2), but would fix itself for later indices.

Here’s the link to the initial activity where I noticed the index issue:

Here’s the link to the second activity which I used to troubleshoot the error:

Thanks!