专题突破
1、(1)-10
(2)1
(3)-18
(4)3.1
(5)-1
(6)-9 1/2
(7)-3 3/4
(8)8.5
(9)0
(10)-10
2、由|a|=21,得a=21或- 21.
由|b|=27,得b=27或-27.
①当a=21,b=27时,|a+b|≠-(a+b).
②当a=21,b=- 27时,|a+b|=-(a+b).
故a-b=21-(-27)=48.
③当a= -21,b=27时,|a+b|≠-(a+b).
④当a=-21,b=-27时,|a+b|=-(a+b).
故a-b= -21- (-27) =6,
故a-b的值为48或6.