Sequence and difference sequence

To a given sequence a(n) = k·n² (green), we want to find its difference sequence Da(n) := a(n+1) - a(n).

1. Use the spreadsheet to create a cell formula which calculates the difference sequence's values in the cells C3 to C30.
2. Plot the first ten elements of the difference sequence with the button in the upper left part of the graphics window. Describe the shape of its graph. How is the graph's slope represented in the spreadsheet?
3. Now vary the sequence's equation with the slider. What happens with the difference sequence? How its slope related to the value of the parameter k?

Andreas Bauer, created with GeoGebra