1、17+-7 1,加法结合律, 连减方法:a+b+c=a+ (b + c ), a+b-c=a +(b-c), a-b+c=a (b-c), a-b-c= a-( b +c);933-15.7-4.3 41.0619.7220.28 73+ 8+2- 11+7+3乘法交换律,连除方法: abc=acba(bc), ab(bc), ac=ac) , ac),700145 18.62.50.4 1.960.54 1.062.5413 29 1258 a+ (b + c )= a+b+c a +(b-c)= a+b-c a (b-c)= a-b+c a-( b +c)= a-b-c;19.68(2.6
2、82.97) 5.68(5.394.32) 19.68(2.979.68) 7+(-) 5-(-)乘法结合律,连除方法. (ab)c= ac)c) = ac, ac, ac) = ac , ac, 1.25( 8 0.5) 0.25( 4 1.2) 1.25( 2130.8) 9.3(4) 0.74(71) 24(-+) (12+) 7 (7-) 0.921.410.928.59 -1.311.61.61.3 11.618.4 9999+999+99+9 4821-998 3.212.525 1.2588 3.60.25 7.60.25 3.50.125 1.8991.8 3.89.90.38 103-2- 1.019.6 1020.87 2.69.9 31+ + 36 38 13.527+13.572+13.5 1.57.4+0.6150%+2 5.3+2.725% 0.6710.16.7 2821.62.816 5.61.70.5683 乘法分配律: (a+b)c+bc (a-b)c-bc 隐“1”法. 拆分法