3x^2≤2
x^2≤2/3
-根号6/3≤x≤根号6/3
2x^2+2x+1>0
2(x^2+x)+1>0
2(x+1/2)^2-1/2+1>0
2(x+1/2)^2>-1/2
因为(x+1/2)^2≥0
所以2(x+1/2)^2≥0
即x∈R