Replace R2 by (−3)R1+R2.

Question

1	4	−4	−4
3	2	7	3
−8	3	6	9

                        (−3)R1+R2

Answer 1

Mentally multiply each entry in row 1 by -3, add those numbers to the corresponding entries in row2, and replace row2 by the results.

So, -3(1) + 3 = 0, -3(4) + 2 = -10, -3(-4) + 7 = 19, and -3(-4) + 3 = 15

Now row 2 is: 0 -10 19 15 and row1 is the same as it was originally.