1、(1)8,-8,-17
(2)2,-2,-5
2、(1)+,-或-,+
(2)-
(3)+
(4)-,-
3、解:(1)(-42)+(+17) = (42 - 17) = 25
(2)0 +(-39.98) = -39.98
(3)(+7.3)+(+3.7)= +(7.3 + 3.7) = 11
(4)(-1/3)+ 0.4 = (-1/3)+ 2/5 = +(2/5 - 1/3) = 1/15
4、解:(1)在数轴上表示如图2-1-7所示。
(-3)+(-4) = (3 + 4) = -7
(2)在数轴上表示如图2-1-8所示。
4 +(-5) = -(5 - 4) = -1