计算:999...9(n个9)*999...9(n个9)+1999...9(n个9)

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计算:999...9(n个9)*999...9(n个9)+1999...9(n个9)计算:999...9(n个9)*999...9(n个9)+1999...9(n个9)计算:999...9(n个9)*

计算:999...9(n个9)*999...9(n个9)+1999...9(n个9)
计算:999...9(n个9)*999...9(n个9)+1999...9(n个9)

计算:999...9(n个9)*999...9(n个9)+1999...9(n个9)
999...9(n个9)*999...9(n个9)+1999...9(n个9)
=999...9(n个9)*【1000...0(n个0)-1】+1999...9(n个9)
=999...9000...0(n个9,n个0)-999...9(n个9)+1999...9(n个9)
=999...9000...0(n个9,n个0)+【1999...9(n个9)-999...9(n个9)】
=999...9000...0(n个9,n个0)+1000...0(n个0)
=1000...0(2n个0)