Given ATA=3I3
(02y12xy−12x−y1)(02x2x2yy−y1−11)=(300030003)
(8x20006y20003)=(300030003)
On comparing the two matrices, we get
8x2=3 and 6y2=3
⇒x2=83 and y2=21
⇒x=±83 and y=±21
For each of x&y we have two possible values, hence there are total 2×2=4 combinations of values are possible.
Hence, total 4 matrices are possible.