7.07x10.8-0.8x7.09=7.07x10.8-0.8x（7.07+0.02）=7.07x10.8-0.8x7.07-0.8x0.02=7.07x（10.8-0.8）-0.016=7.07x10-0.016=70.7-0.016=70.684
