计算89-899+8999-89999+...+89999999=

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计算89-899+8999-89999+...+89999999=

计算89-899+8999-89999+...+89999999=
计算89-899+8999-89999+...+89999999=

计算89-899+8999-89999+...+89999999=
=(90-1)-(900-1)+(9000-1)-...+(90000000-1)
=90-1-900+1+9000-1-90000+1...+90000000-1
=90-900+9000-90000+900000-9000000+90000000-1
=(90+9000+900000+90000000)-(900+90000+9000000)-1
=90909090-9090900-1
=81818190-1
=81818189