(x-1)(x+1)=x2-1
(x-1)(x2+x+1)=x3-1
(x-1)(x3+x2+x+1)=x4-1
根据前面各式的规律可得
(x-1)(xn+xn-1+…+x+1)=_____.
xn+1-1
(4)(5x+3y)・( )=25x2-9y2
(5x-3y)
(5)(-0.2x-0.4y)( )=0.16y2-0.04x2
(-0.4y+0.2x)
(6)(-x-11y)( )=-x2+121y2
(-11y+x)
若(-7m+A)(4n+B)=16n2-49m2,则A= ,B= .
4n,7m
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