12345679


                                              1=        1
           1×9+
=       10
          11×9+
=      100
         111×9+
=     1000
        1111×9+
=    10000
       11111×9+
=   100000
      111111×9+
=  1000000
     1111111×9+
= 10000000
 +)
 11111111×9+1=100000000
    12345678×9+
=111111111

因為 12345678×9+9=(12345678+1)×9=12345679×9,所以 12345679×9=111111111 。因此

12345679×18=222222222
12345679×27=333333333
12345679×36=444444444
12345679×45=555555555

12345679×54=666666666
12345679×63=777777777
12345679×72=888888888
12345679×81=999999999

                                                                          

因為$\frac{1}{81}$=$\large\frac{12345679}{999999999}$=0.012345679,可知(1÷81)×90.1,(1÷81)×9×20.2,.....,(1÷81)×9×90.91

 


Copyright © 昌爸工作坊 all rights reserved.