What is the variable in this algebraic expression $7d+2$ ?

Hint: To find the variable in the algebraic expression $7d+2$ , one must know the definition of a variable. A variable is an alphabet which is used to represent the unknown number.

Complete step-by-step solution:
We have to find the variable in the algebraic expression $7d+2$ . Let us recollect what a variable is. A variable is an alphabet which is used to represent the unknown number. A variable can be dependent and independent. A dependent variable is a variable that depends on the value of some other number or variable. We can say that a dependent variable is the output of a function. An independent variable does not depend on any values. We can say that it is the input of a function.
Hence, from the given expression, we can see that d is a variable. To be clearer, d is an independent variable.

Note: Students may get confused with variables and constants. We have seen what variables are and their types. Let us see an example of a dependent variable. Consider a function $y=7d+2$ . Here, y is a dependent variable while d is an independent variable. A constant is a fixed value, which is used in algebraic expressions and equations. A constant does not change over time and has a fixed value. In the given expression $7d+2$ we can see that 2 is a cons