(x-2y)的平方- (x+2y)的平方=[(x-2y)+(x+2y)][(x-2y)-(x+2y)]=(2x)(-4y)=-8xy
(x-2y)的平方- (x+2y)的平方 平方差公式
=(x-2y+x+2y)(x-2y-x-2y)
=2x *-4y
=-8xy
(x-2y)^2-(x+2y)^2
=x^2-4xy+4y^2-x^2-4xy-4y^2
=8xy
或
(x-2y)^2-(x+2y)^2
=((x-2y)+(x+2y))((x-2y)-(x+2y))
=4y*2x
=8xy
(x-2y)2-(x+2y)2=[(x-2y)+(x+2y)][(x-2y)-(x+2y)]
=2x*(-4y)
=-8xy
(x-2y)^2- (x+2y)^2
=[(x-2y)+ (x+2y)]*[(x-2y)- (x+2y)]
=2x * (-4y)
=-8xy
(x-2y)^2-(x+2y)^2=[(x-2y)+(x+2y)]*[(x-2y)-(x+2y)]
= -8xy