(99-999+9999-99999+999999)x9
=[(100-1)-(1000-1)+(10000-1)-(100000-1)+(1000000-1)]x9
=[(100-1000+10000-100000+1000000)-1]x9
= 909100x9-9
= 8 181 891
其实直接算已经很简单了~
(99-999+9999-99999+999999)x9
=(99+9000+900000)x9
=909099x9
=8181891
(99-999+9999-99999+999999)x9
=[(100-1)-(1000-1)+(10000-1)-(100000-1)+(1000000-1)]x9
=[(100-1000+10000-100000+1000000)-1]x9
= 909100x9-9
= 8 181 891
其实直接算已经很简单了~
(99-999+9999-99999+999999)x9
=(99+9000+900000)x9
=909099x9
=8181891