乘法交换律:A×B=B×A乘法结合律:(A×B)×C=A×(B×C)乘法分配律:(A+B)×C=A×C+B×C,除法:a÷b÷c=a÷(b×c),a÷b×c=a÷(b÷c),a÷(b×c)=a÷b÷c,a÷(b÷c)=a÷b×c,a÷b×c=a×c÷b,注:(除法去扩号添括号要变符号)。