赚现金
观察下列各式的规律:
( x - 1 ) ( x + 1 ) = x 2 - 1
( x - 1 ) ( x 2 + x + 1 ) = x 3 - 1
( x - 1 ) ( x 3 + x 2 + x + 1 ) = x 4 - 1
…
可得到 ( x - 1 ) ( x 7 + x 6 + x 5 + x 4 + x 3 + x 2 + x + 1 ) = ;
一般地 ( x - 1 ) ( x n + x n - 1 + x 5 + … + x 2 + x + 1 ) = .
试题篮