Which statement is true regarding constants?

Constants are defined as values that do not change regardless of the variables in an equation or expression. This means that in any mathematical context, whether it be algebra, calculus, or other fields, a constant will always retain its defined value. For example, in the equation y = 3x + 2, the number 2 is a constant; it remains unchanged irrespective of the value of x.

In contrast to constants, variables can take on different values, and that's what differentiates them. The stability of constants makes them fundamentally important in equations, as they serve as reference points or fixed values around which variables can operate.

When considering the other options, a statement about constants varying based on an equation would be inherently incorrect, as constants do not change. Similarly, while constants might be used in inequalities, they are not essential for forming them, as you can have inequalities that primarily involve variables. Moreover, while constants can appear in linear equations, they are not limited to this context; they are present in various types of equations and mathematical expressions. Thus, the definition and role of constants affirm that they remain unchanged, confirming the correctness of the statement.