Not sure if it is rounding but I get the sums as follows:

sum(x1*y*) = 21.3945

sum(x2*y*) = -21.3195

sum(x1*x2*) = 0

x1*^2 = x2*^2 = 20

With these I was able to match the prior posts answers as well as Excel. Hopefully this helps solve your problem.

Also, I have been using the linest function in Excel and I am not sure how to 1. separate the results in different cells and 2. determine which each comma separated result is. Any ideas? Thanks!