A question about "an empty set is a subset of an empty set" If we judge by "any set is a subset of itself", an empty set is a subset of an empty set. That is to say, an empty set is an element of an empty set According to the definition of an empty set, a set without any elements is called an empty set?

A question about "an empty set is a subset of an empty set" If we judge by "any set is a subset of itself", an empty set is a subset of an empty set. That is to say, an empty set is an element of an empty set According to the definition of an empty set, a set without any elements is called an empty set?

An empty set is a subset of an empty set. Yes, but an empty set is not an element of an empty set. If there is no element in an empty set, it is not an empty set, but a set containing a set

The process of proving that the number of subsets of a set is equal to 2n power
Such as the problem, a set of subsets equal to the number of n-th power of 2 proof process, do not enumerate method, hope that a master can use mathematical derivation formula to help me push down, thank you!

What is cos2a