18.9x178.178+0.49-17.8x189.189

18.9x178.178+0.49-17.8x189.189
18.9x178.178+0.49-17.8x189.189

18.9x178.178+0.49-17.8x189.189
18.9x178.178+0.49-17.8x189.189
=189x17.8189-17.8x189.189+0.49
=(189x17.8+189x0.0189)-17.8x189.189+0.49
=17.8x(189-189.189)+17.8x0.0189+0.49
=17.8x0.0189-17.8x0.0189+0.49
=0.49

=18.9*(178+0.178)+0.49-17.8*(189+0.189)=18.9*178+18.9*0.178+0.49-17.8*189-17.8*0.189=0.49。
因为18.9*178-17.8*189=0，并且18.9*0.178-17.8*0.189=0。

18.9x178.178+0.49-17.8x189.189
=18.9x17.8x10.01-17.8x18.9x10.01+0.49
=0.49

18.9*178.178+0.49-17.8*189.189
=18.9*10.01*17.8+0.49-17.8*18.9*10.01
=18.9*10.01*17.8-17.8*18.9*10.01+0.49
=(18.9*10.01*17.8-17.8*18.9*10.01)+0.49
=0.49

ABAB可以写成AB*101
ABCABC可以写成ABC*1001
以次类推