A set without any elements is called an empty set, and it is recorded as (as shown below, I can't make it bigger). Like equation x? 6 = 0 has no solution in the real number range, that is, the solution set is an empty set, the intersection of two parallel lines, a triangle whose sum of two sides is less than the third side, etc. They are all empty sets.

But 0 does not belong to an empty set, and {0} is a set with one element 0, also known as a single element set, 0∈{0}.

Question 1: x? There is a set of -2x+ 1=0, because actually several roots are solved, X 1= 1, X2= 1. According to the mutual dissimilarity of elements (that is, every element that constitutes a set should be different from each other, and the elements in the set cannot appear repeatedly, that is, the same can only be counted as one. For example, the set {2,2,3} means that it is wrong, and the correct representation is {2,3}. )

So all the real roots of this equation have only one set, which is {1}.

Question 3: Certainty means that whether any object in nature is an element of this set is clear, either affirmative or negative. For example, integers greater than 4 can form a set, 5 is an element of this set, and 3 is not an element of this set. It is very clear that there is no ambiguity.