Set c is a single element set.
∴ simultaneous a and b, get: a | x | = x+a.
(1) when x >; 0, X=a/(a- 1)>0, found one.
(2) when x < 0 and x =-a/(a+ 1) < 0, find a.
(3) When X=0, find a=0.
∴ To make C a single element set, it is necessary to (1)(2)(3) not have two different solutions at the same time.
- 1 & lt； a & lt 1.