51.8-1.8*（2.03-0.18）=51.8-（2-0.2）*（2+0.03-0.2+0.02）=51.8-（2-0.2）*（2-0.2+0.05）=51.8-（2-0.2）*（2-0.2）-（2-0.2）*0.05=51.8-4+2*0.2*0.2-0.04-0.1+0.01=47.8+0.08-0.04-0.1+0.01=47.7+0.05=47.75
