1
若x+y=2a,x-y=2b,
x²－y² 平方差
=(x-y)(x+y)
=2a×2b
=4ab
2
(x²+1/4)(x+1/2)(x-1/2)
=(x²+1/4)[(x+1/2)(x-1/2) ] 平方差
=(x²+1/4)(x²-1/4) 平方差
=x^4-1/16
3
A.2009²-2008×2010
=2009²-(2009-1)×(2009+1) 平方差
=2009²-(2009²-1²)
=1
B.2009²－2009×2010
=2009×(2009-2010)
=-2009
C.2009²－2009×2008
=2009×(2009-2008)
=2009
D.2009²－2008² 平方差
=(2009-2008)(2009+2008)
=4017
选A