Answer:
[tex]f(x) = 1588.4x + 39000[/tex]
[tex]f(15) = 62826[/tex]
Step-by-step explanation:
Given
In 1990; Income= $39000
In 2010; Income= $70768
Solving (a): An equation in form of f(x) = ax + b
First, we need to determine the slope, a
[tex]a = \frac{y_2 - y_1}{x_2 - x_1}[/tex]
Taking y as income and x as year index.
When x = 0; y = 39000
When x = 20; y = 70768
Substitute these values in the above formula
[tex]a = \frac{70768 - 39000}{20 - 0}[/tex]
[tex]a = \frac{31768}{20}[/tex]
[tex]a = 1588.4[/tex]
Next, is to determine the formula using:
[tex]y - y_1 = a(x - x_1)[/tex]
Considering :When x = 0; y = 39000, we have
[tex]y - 39000 = 1588.4(x - 0)[/tex]
[tex]y - 39000 = 1588.4x[/tex]
Make y the subject of formula
[tex]y = 1588.4x + 39000[/tex]
Express y as a function of x
[tex]f(x) = 1588.4x + 39000[/tex]
Solving (b): Income in 2005
In 2005, x = 15
So:
[tex]f(x) = 1588.4x + 39000[/tex] becomes
[tex]f(15) = 1588.4 * 15 + 39000[/tex]
[tex]f(15) = 62826[/tex]