(3m-n+2)(3m-n-2)
=[(3m-n)+2][(3m-n)-2]
=(3m-n)²-2²
=9m²-6mn+n²-4
2011²-2010×2012
=2011²-(2011-1)(2011+1)
=2011²-(2011²-1²)
=2011²-2011²+1²
=1²
=1
(3m-n+2)(3m-n-2)
=[(3m-n)+2][(3m-n)-2]
=(3m-n)²-2²
=9m²-6mn+n²-4
2011²-2010×2012
=2011²-(2011-1)(2011+1)
=2011²-(2011²-1²)
=2011²-2011²+1²
=1²
=1