I am trying to understand the calculation of a quadratic regression in Excel in order to break it down step by step into individual calculation steps.The aim is that each step of the calculation is performed individually in a column. The calculation comes from an Excel forum from over 10 years ago.

The calculation is as follows:

G1 = INDEX(LINEST(E$2:E$6;D$2:D$6^{0.1.2};0;0);ROW())
G2 = INDEX(LINEST(E$2:E$6;D$2:D$6^{0.1.2};0;0);ROW())
G3 = INDEX(LINEST(E$2:E$6;D$2:D$6^{0.1.2};0;0);ROW())

G9 = "y = " &TEXT(G1;"0,0##x²;- 0,0##x²;""""")&" "&TEXT(G2;"+ 0,0##x;- 0,0##x;""""")&" "&TEXT(G3;"+ 0,0##;- 0,0##;""""")

Picture of the Calculation in Excel

I am trying to understand the index and LINEST function (like in G1). What happens in it?

I understand that at the end all three calculations for the quadratic equation are put together. But how is the calculation done for the individual three parts? Which steps are carried out step by step? Variance? Correlation? What happens in the formula?

I know that Excel also offers a help file for the LINEST function, but it doesn’t help me either.
I would be very happy about help.