9×1/36+12×1/48+15×1/75+18×1/90+21×1/126+27×1/144+27×1/216+30
12,9,21,27,15,60,3,1,18
1/18+1/36+1/60+1/90+1/126+1/168+1/216(用裂项的方式)
5/6+5/18+5/36+1/12+1/18+5/126+5/168+5/216+1/54=?
1+9+18+27=?
8/9*15/36+1/27简算 有过程
16-1=15;25-4=21;36-9=27;49-16=33,.
1*3*9+5*15*45+3*9*27+2*6*18+4*12*36分之5*10*20+1*2*4+3*6*12+2*
找规律填空 1 3 9 27 [ ] 1 2 4 8 [ ] 32 15 21 18 19 21 17[ ] [ ]
1 5 12 21 27 ( )
1,8,27,( )125,216,括号里填几?
1,8,27,64,,216,343
按 1,8 ,27 ,( ) ,125,216