C 1 CAm 1+ktm Am-1 CAm-2 1+kt m-1 40 i=1 因为xm C40-Cm=1- Am 1+kT2 C C cy 1 m 1+kt 等比数列 i= 1+ki, 400 1 1 1 m Am A i i C C k =  = + 1 1 2 1 2 1 2 1 0 1 1 1 1 1 . 1 1 1 1 Am Am m Am Am m A A A A C C k C C k C C k C C k     − − − − = + = + = + = + 1 1 1 1 m m i i x = k = − + 0 0 0 1 A Am Am m A A C C C x C C − 因为 = = − 等比数列