初中代数求值1/5+1/45+1/117+1/221+1/357
1/5+1/45+1/117+1/221+1/357=?
1/5+1/45+1/117+1/221+1/357 =1/5+(1/5-1/9)/4+(1/9-1/13)/4+(1/13-1/17)/4+(1/17-1/21)/4 =1/5+1/5/4-1/21/4 =5/21