显然a=0时,A=∮,不满足条件。a>0时,易知f(0)=0,x>0时,f(x)=x(1+a|x|)>0,于是f(0+a)>f(0),而由已知[–1/2,1/2]在于A可得0∈A,即f(0+a)
分类讨论,四类,1,x+a>=0且x>=0 ,2,x+a>=0且x<=0,3,x+a<=0且x<=0,4,x+a<=0且x>=0,分别用这四种化简绝对值号,然后将所有的结果合并
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