Question

In matrix product HF, the value in the fourth row of the first column is
[1 0 ]
[4 -3] = F
[-2 6]
[-1 5]

[1-2 -1 3]
[2 0 4 -1] =H
[3 5 -2 2]
[1-1 0 0]

Answer 1

It's the dot product of the fourth row of H and the first column of F