Example:a={xx2+1=0, and is an real number}, No element empty set, JA =0 The set that has no elements in it is denoted by { or the symbol and is called the empty set. Note:{} is not an empty set. It is set with one element which the element is the empty set. DE{), but universal set The universal set is the set of all elements under consideration in a given discussion. We denote the universal set by U.Example:A={x|x2+1=0, and x is an real number}, No element empty set,|A|=0. The set that has no elements in it is denoted by {} or the symbol  and is called the empty set. Note: {} is not an empty set. It is a set with one element which the element is the empty set. {}, but . universal set The universal set is the set of all elements under consideration in a given discussion. We denote the universal set by U