0.9×9.9×99.9×999.9得0.9×9.9×99.9×999.9=我当然会用,不过要求用简便算法,要不然我问什吗啊

Question

0.9×9.9×99.9×999.9得
0.9×9.9×99.9×999.9=
我当然会用,不过要求用简便算法,要不然我问什吗啊

Answer 1

0.9×9.9×99.9×999.9
=0.9×(10-0.1)×(100-0.1)×(1000-0.1)
=(9-0.9)×(100-0.1)×(1000-0.1)
=8.1×(100-0.1)×(1000-0.1)
=(810-0.81)×(1000-0.1)
=809.19×(1000-0.1)
=809190-80.919
=809109.081