4.2×9.8+0.84=4.2×9.8+4.2×0.2=4.2*（9.8+0.2）=4.2*10=42
4.2x9.8+0.84简便计算如下：4.2x9.8+4.2x0.2=4.2x（9.8+0.2）=4.2x10=42
