4a?-(x+y)?
4a?-(x+y)?=(2a)?-(x+y)?=[2a+(x+y)][2a-(x+y)]=(2a+x+y)(2a-x-y)
1-9b?
1-9b?=1-(3b)?=(1+3b)(1-3b)
(x+y)?-1
(x+y)?-1=(x+y+1)(x+y-1)
4a?-(x+y)?
4a?-(x+y)?=(2a)?-(x+y)?=[2a+(x+y)][2a-(x+y)]=(2a+x+y)(2a-x-y)
1-9b?
1-9b?=1-(3b)?=(1+3b)(1-3b)
(x+y)?-1
(x+y)?-1=(x+y+1)(x+y-1)