2×9=18 9²=81 2×99=198 99²=9801 2×999=1998 999²
9*9=81 99*99=9801 999*999=998001 100个9*100个9=?n个9*n个9=?
99^2=9801 999^2=998001 9999^2=99980001 99999^2=9999800001
999+99+9=?
99×99=9801 999×999=998001 的规律
9+99+999+9999+99999 = =
1²-2²+3²-4²+.+99²-10²=101²
99999/2+9999/2+999/2+99/2+9/2=
100²-99²+98²-97²+……+2²-1²=?
计算100²-99²=98²-97²+...+2²-1²的值
100²-99²+98²-97²+...+2²-1²= (急
求和:Sn=1²-2²+3²-4²+5²-6²+...+99
若S=1²-2²+3²-4²+...+99²-100²+10