Question

9999X9999X19999简便方法？

Answer 1

9×9=81
99×99=99×（100-1）=9801
999×999=99×（1000-1）=998001
9999×9999=9999×（10000-1）=99980001
原式=9999×9999×19999
=99980001×（20000-1）
=99980001×20000-99980001
=1999500039999

Answer 2

(10000-1)x(10000-1)x19999
=(100000000-2x10000+1)x(20000-1)
=100000000x(20000-1)-(20000-1)x(20000-1)
=2000000000000-100000000-(400000000-2x20000+1)
=2000000000000-100000000-(400000000-40000+1)
=2000000000000-500000000+40000-1
=1999500040000-1
=1999500039999

Answer 3

9999×9999×19999
=(10000-1)(10000-1)×19999
=(100000000-20000+1)19999
=100020001(20000-1)
=2000400020000-100020001
=1999500039999

Answer 4

计算器最简便

Answer 5

X代表10000算式：
(X-1)(X-1)(2X-1)
＝2X立方-5X平方+4X-1