即:x∑P(x)1-∑P(x)14= ∑P(x)-2x∑(x)t+∑P(x) =0 1:xP(x)-B(x)=(+1)1-2xB+(1-1)P 即(7+1)P1-(21+1)xP(x)+P1(x)=0 问:如何证(2)?答: d(*) 2xt+t )32( ) ( ) 1 0 0 - l l l l l l x P x t P x t ¥ ¥ + = = 即: å å = ( ) ( ) ( ) -1 1 0 0 0 - 2 l l l l l l l l l lP x t x lP x t lP x t ¥ ¥ ¥ + = = = å å å+ ( ) ( ) ( ) ( ) -1 1 -1 : - 1 - 2 -1 l l l l l l t xP x P x = l + + P+ xlP l P 即(l +1) Pl+1 - (2l +1 0 ) xPl l ( x) + = lP x -1 ( ) 问：如何证(2)？答： ( ) ( ) 3 2 0 2 1 - 2 l l l t P x t xt t ¥ = = å ¢ + d dt (*)