0.78=? 0.78=7.8*0.1!!!然后干嘛?提取公因式
7.8*9.9+0.78=7.8*9.9+7.8*0.1=7.8*(9.9+0.1)=7.8*10=78
=7.8*(10-0.1)+0.78=78-0.78+0.78=78
7.8*9.9+0.78=7.8*(10-0.1)+0.78=78-0.78+0.78=78
0.78(10*9.9+1)=0.78(99+1)=0.78*10078