The value of a variable can change, depending on the situation or problem being considered. For example, in the equation y = 2x + 3, x is a variable that can take on different values depending on what we want to solve for.

On the other hand, a constant is a value that does not change. It is a fixed value in an equation or formula that remains the same, no matter what the problem is. Constants are often represented by letters, such as c or k, and their value is usually known or defined. For example, in the formula for the circumference of a circle, C = 2πr, π (pi) is a constant that represents the ratio of a circle's circumference to its diameter.

The main difference between variables and constants is that variables can change, while constants remain fixed. Variables can be used to represent unknown values that we want to solve for, while constants are known values that are used in calculations. In mathematical expressions and equations, variables and constants are both essential components that work together to solve problems and provide solutions.