1.4: Intersection of Straight Lines . Linear Function DEFINITION 1. A function, f, is a rule that assigns to each value of r one and only one value of y: y = f(x). The variable r is referred to as the independent variable ( the "input"). The variable y is referred to as the dependent variable ( the "output"). We will use linear functions (those that can be represented graphically by a line) to create linear models. DEFINITION 2. The function f defined by f(x) = mr +b where m and b are constants, is called a linear function. . Linear Depreciation: - An item has an initial value and a final value. - Assume the value decreases linearly with time: V (t) = mi + b. To solve linear depreciation problems: find points - find equation of line - answer question. EXAMPLE 3. Bob bought a car three years ago that is currently valued at $9, 800. Five years from now it will be worth $6200. Assuming it is linearly depreciating, how much was his car worth when he bought it