(1).(x+2y)^2-(x-2y)^2
=[(x+2y)+(x-2y)][(x+2y)-(x-2y)]
=2x*4y
=8xy
(2).(a-b+1)^2
=[(a-b)+1]^2
=(a-b)^2+2(a-b)+1
=a^2-2ab+b^2+2a-2b+1