【正文】
nmmnmjj aaaa ???? ??? ?1Example 10. Example 13. (Double summation) 552516941512 ????????jj60)4321(66)32(41414131????????? ??? ???? ? iii jiiiiijGeneralized Summations ? For an infinite series, we may write: ? To sum a function over all members of a set X={x1, x2, …}: ? Or, if X={x|P(x)}, we may just write: . . .: 1 ??? ???? jjjii aaa. . .)()(:)( 21 ?????xfxfxfXx. . .)()(:)( 21)(???? xfxfxfxPSimple Summation Examp