即x(n+1)=142 )",n≥-2 0 n<-2 x(n+1 1/2 1/8 n  −  − + = 0, 2 ) , 2 21( 41 ( 1 ) nn x n n 即 1/2 1/4 1/8 1 x(n+1) n - 2 - 1 0 1