factor out 3
3(a^2-8ab + 16b^2)
then imagine b's were not there
3(a^2-8a +16) use pefect square trinomial pattern... or factors of 16 that add to = -8 uhm -4 and -4
Wrte factors with space to remember the b's
3(a-4 )(a-4 )
remember the b's
multiply out and check the b's will generate the ab term and the b squared term.