設(shè)a>0,函數(shù)
,給出下列四個(gè)結(jié)論:
①當(dāng)a=2時(shí),f(x)在(-∞,0)上單調(diào)遞增;
②當(dāng)a≥1時(shí),f(x)存在最大值;
③設(shè)M(x
1,f(x
1))(x
1≤a),N(x
2,f(x
2))(x
2>a),則|MN|>1;
④若y=f(x),y=-x的函數(shù)圖象有三個(gè)公共點(diǎn),則a的取值范圍是(0,1).
其中所有正確結(jié)論的序號(hào)是
①②③④
①②③④
.