2.三点公式 n=2时(xk)=L2(x)+E2(xk)k=0,1,2 x-Xo(x L2(x)=fo (x-x1)(x-x2)c(x-x0)(x-x2)c( X1 2 1 x-x1)+ xx+x-x x-xo+(x I2(x)=f0 f1 +f2 (x-x)(x-x2)(x1-x0)(x1-x2)“2(x2-x)( X -x (3) E2(rk) ∏I(xk-x) k 若x,x1x2为等距节点,即h=x1-x=x2-x1,则2.三点公式 n = 2时 ( ) ( ) ( ) k 2 k 2 k f ¢ x = L¢ x + E x k = 0,1,2 ( )( ) ( )( ) ( )( ) ( )( ) ( )( ) ( )( ) ( ) 2 0 2 1 0 1 2 1 0 1 2 0 2 1 0 1 0 2 1 2 2 0 x x x x x x x x f x x x x x x x x f x x x x x x x x L x f - - - - + - - - - + - - - - = ( )( ) ( ) ( ) ( )( ) ( ) ( ) ( )( ) ( ) ( ) ( ) 2 0 2 1 0 1 2 1 0 1 2 0 2 1 0 1 0 2 1 2 2 0 x x x x x x x x f x x x x x x x x f x x x x x x x x L x f - - - + - + - - - + - + - - - + - ¢ = Õ ¹ = = - 2 0 (3) 2 ( ) 3! ( ) ( ) j k j k k j x x f E x x 若 x0 , x1 , x2为等距节点，即h = x1 - x0 = x2 - x1，则