a Notice that amount of money on the checking account will decrease each month by $8.
B
b Use the linear equation found in Part A. In order to find the intercepts, substitute 0 for each of the variables. Then solve the equation for the other variable.
A
aFunction: f(x)=360-8x
Graph:
B
bx-intercept: 45
y-intercept: 360 Interpretation: See solution.
Practice makes perfect
a We want to write and graph the equation that gives the balance f(x) in dollars of the abandoned checking account. Notice that the bank charges an $8 monthly fee for the account. Therefore, the $360 on the bank account decreases by $8 every month. Knowing this, we can write an equation f(x), where x represents the number of months.
f(x)= 360- 8xNext, we can use this linear equation to create a table of x- and f(x)-values. This way we will find the points lying on the graph of the equation. Notice that we can choose any positive x-values to find the points.
x
f(x) = 360-8x
f(x)
Point
10
360-8( 10)
280
( 10, 280)
20
360-8( 20)
200
( 20, 200)
30
360-8( 30)
120
( 30, 120)
40
360-8( 40)
40
( 40, 40)
Finally, we can graph the equation by plotting the points and connecting them with a straight line.
b Now we want to find and interpret the x- and y-intercepts. Let's start with the x-intercept. To find it, we will substitute 0 for f(x) and we will solve the equation for x.
The x-intercept is 45. This means that, after 45 months, the money in the bank account will be $0. Now, we will find the y-intercept by substituting 0 for x and solving for f(x).
