3.
非空数集\(A\)如果满足:\(①0∉ A\);\(②\)若对\(∀ x∈A\),有\(\dfrac{1}{x}∈A\),则称\(A\)是“互倒集”\(.\)给出以下数集:
\(①{x∈R∣x^{2}+ax+1=0}\);\(②\{x∣{x}^{2} -4x+1 < 0\}\);
\(③\{y|y= \dfrac{\ln x}{x},x∈[ \dfrac{1}{e},1)∪(1,e]\} \);
\(④\left\{ y\left| y=\left\{ \dfrac{2x+\dfrac{2}{5},x\in [0,1)}{x+\dfrac{1}{x},x\in [1,2]} \right. \right. \right\}\).
其中“互倒集”的个数是________.