3.证明x0-xr本=x0-xk 证明：令1-x=t [x"(-x)"&=f"A-P(-d) =∫x-x1 1 0 0 3 (1 ) (1 ) m n n m x x dx x x dx − = −   .证明： 证明：令1− = x t 1 0 (1 ) n m = − x x dx  1 0 0 1 (1 ) (1 ) ( ) m n m n x x dx t t dt − = − −  