Consider the set *THE* = {0, 1, 2, 3, 4, 5} and the equation **x + 2 = 5**.

Note that set number 3 *THE* is called **universe set** of the equation and the set {3} is the **truth set** of this same equation.

Note this other example:

Determine the integers that satisfy the equation

**x² = 25**.

The set of integers is the universe set of the equation. The numbers -5 and 5, which satisfy the equation, form the truth set and can be indicated by:

V = {-5.5}.

Hence, we conclude that:

**Universe set**is the set of all values the variable can assume. It is indicated by

**U.**

**Truth set**is the set of values of

**U**that make the equation true. It is indicated by

**V**.

**Comments:**

- The truth set is a subset of the universe set.

- Not being mentioned the universe set, we must consider as a universe set the set of rational numbers.

*The truth set is also known as***solution set**and may be indicated by**s**.

*Next: Roots of an Equation*