99999...(2000个9)×99999...(2000个9)
=【1000...(2000个0)-1】×99999...(2000个9)
=99999...(2000个9)00000...(2000个0)-99999...(2000个9)
=99999...(1999个9)8(1个8)0000...(1999个0)1(1个1)
99999...(2000个9)×99999...(2000个9)
=【1000...(2000个0)-1】×99999...(2000个9)
=99999...(2000个9)00000...(2000个0)-99999...(2000个9)
=99999...(1999个9)8(1个8)0000...(1999个0)1(1个1)