用字母a、b、c表示如下运算定律:加法交换律______;加法结合律______;乘法交换律______;乘法结合律______;乘法分配律______.
例如:加法交换律: 2+3=5, 3+2=5, a+b=b+a; 加法结合律: 1+2+3, =(1+2)+3, =3+3, =6, 1+2+3, =1+(2+3), =1+5, =6, (a+b)+c=a+(b+c); 乘法交换律: 2×3=6, 3×2=6, a×b=b×a; 乘法结合律: 2×3×5, =(2×3)×5 =6×5 =30, 2×3×5, =2×(3×5), =2×5, =30, (a×b)×c=a×(b×c); 乘法分配律: 5×(2+4), =5×6, =30, 5×(2+4), =5×2+5×4, =10+20, =30, a×(b+c)=a×b+a×c; 故答案为:a+b=b+a;(a+b)+c=a+(b+c);a×b=b×a;(a×b)×c=a×(b×c);a×(b+c)=a×b+a×c. |