when domain is all real numbers?

 A domain of all real numbers includes all possible values of a variable that can be expressed as a real number. Real numbers include all rational numbers (integers, fractions, and repeating decimals), as well as irrational numbers such as pi and the square root of 2. In addition, real numbers also include positive infinity, negative infinity, and all the numbers in between. This means that the domain of all real numbers is the set of all the possible values that a variable can take on, including all rational and irrational numbers.