What is the proper mathematical term for the symbol used to represent a missing addend in an equation?

The correct term for the symbol used to represent a missing addend in an equation is a variable. In mathematics, a variable is a symbol, often represented by a letter, that stands in for an unknown value or a value that can change. When solving equations, especially those involving addition, a variable can be used to denote an addend whose value is not yet known, allowing us to express relationships and perform algebraic operations.

For instance, in the equation (x + 5 = 12), (x) is the variable that represents the missing addend. By manipulating the equation, we can solve for (x) and determine its value, which adds clarity to the relationship among the numbers in the equation.

This understanding is crucial as it forms the foundation for algebraic thinking and problem-solving, enabling students to work with equations more flexibly. Other terms, such as constant, coefficient, and expression, refer to different mathematical concepts and do not accurately describe a symbol representing a missing addend. A constant is a fixed value, a coefficient indicates a multiplicative factor attached to a variable, and an expression refers to a combination of numbers and variables without an equality sign.