How one can keep same-row cell (or same-column cell) constant in a formula
while he/she uses drag-fill handle?
There is a formula in B2: =A2+B1. We want to use drag-fill to fill:
- row 2 while keeping A2 the same, and,
- column B while keeping B2 the same
(changing A2 to $A$2 is not helpful)

A B C D E F G
_____________________
1 |__|__|__|__|__|__|__|_
2 |__|__|__|__|__|__|__|_
3 |__|__|__|__|__|__|__|_
4 |__|__|__|__|__|__|__|_
5 |__|__|__|__|__|__|__|_
6 |__|__|__|__|__|__|__|_