1、12.065.072.94 30.349.7610.34 33 2574 3441.7 1.250.8 1027.35.1 17+-7 1,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+3abc=a(bc), abc=a(bc), abc=a(bc) , abc=a(bc),700145 18.62.50.4 1.960.54 1.062.5413 29 a+ (b + c )= a+b+c a +(b-c)= a+b-c
2、a (b-c)= a-b+c a-( b +c)= a-b-c;19.68（2.682.97） 5.68（5.394.32） 19.68（2.979.68） 7+(-) 5-(-)a(bc) = abc, a(bc) = abc, a(bc) = abc , a(bc) = abc, 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 4821-9983.212.525 1.2588 3.60.25 7.60.25 3.50.125 1.8991.8 3.89.90.38 103-2- 1.019.61020.87 2.69.9 31+ + 36 3813.527+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
