# How to Write an Equation for a Function

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In mathematics, an equation is an expression that equates two values on either side of an equal sign. From the equation, you can determine the missing variable. For example, in the equation "3 = x - 4," x = 7. However, a function is an equation in which all of the variables are dependent upon the independent numbers in the mathematical statement. For instance, in the function "2x = y," y is dependent upon the value of x to determine its numerical worth.

Determine the value of your function. The value of the independent variable never changes in a series of functions, enabling you to graph your findings. For instance, if your function is "3x = 15," you will know that x = 5 for all of your subsequent functions in that set.

Think of the function in terms of purchases. For instance, if you buy one case of ramen, you will pay $5. However, if you change the number of cases you purchase, the total spent will change. Thus, three cases of$5 ramen will cost \$15 and the overall cost is dependent on the number of items purchased. It is not dependent on the cost of each individual item, which is constant. You may graph this or represent the values in a table in order to keep the information organized.

Represent the function as an equation that may be used for any added value to determine the cost of a purchase. This equation will be the inverse of the function equation that you started out with, which was 3x = 15. Instead, now that you know that x = 5, you can replace the numbers with variables to allow the values to be adjusted according to the needs of the problem solver. Therefore, v5 = c. This means that any value multiplied by five will give you the cost of that number of items.