5.8x3.7+0.58x0.21=5.8x（3.7+0.021）=5.8x3.721=21.5818
=2.9*7.4+0.29*0.42=7.4（3-0.1）+0.42（0.3-0.01）=22.2-0.74+0.126-0.0042=22.2-0.74+0.1218=22.2-0.6182=21.5818
