199.199×198-198.198×199
=199×1.001×198-198×1.001×199
=0
18.9×178.178+0.49-17.8×189.189
=18.9×(178×1.001)+0.49-17.8×(189×1.001)
=18.9×178×1.001-17.8×189×1.001+0.49
=18.9×178×1.001-178×18.9×1.001+0.49
=0+0.49
=0.49
199.199×198-198.198×199
=199×1.001×198-198×1.001×199
=0
18.9×178.178+0.49-17.8×189.189
=18.9×(178×1.001)+0.49-17.8×(189×1.001)
=18.9×178×1.001-17.8×189×1.001+0.49
=18.9×178×1.001-178×18.9×1.001+0.49
=0+0.49
=0.49