What characterizes an equation?

An equation is fundamentally characterized as a mathematical sentence that includes an equals sign. This means it expresses a relationship between two expressions that are equal in value. The equals sign serves as a critical indicator that the values on either side of it are balanced or that one side is equivalent to the other.

For instance, in the equation 3 + 2 = 5, the left side (3 + 2) is equal to the right side (5), demonstrating the concept of equality. This defining feature is essential to understand various mathematical concepts, including solving for unknowns within algebraic equations.

The other options do not capture the essence of what constitutes an equation. A mathematical statement that shows inequality indicates a different relationship altogether and involves symbols like "<" or ">", which signify that one value is not equal to another. The total sum of numbers refers to an operation rather than a structural definition; it describes what happens in calculations but does not represent the equality aspect. Lastly, a representation using only one variable is too restrictive and does not encompass the broader definition of equations, which can involve multiple variables or constants.