linear equation

Question

The salary of a person was $45,000 in 2009 and $48,000 in 2001.

 

A) find a linear equation to determine the salary y of the person in year x.

 

B) Write the equation in (a) as a slope- intercept form.

Answer 1

Let x = time
Let y = salary
 
 
We can set up the information as coordinates on a graph.
 
P₁ = (2009, 45000)
P₂ = (2001, 48000)
 
Lets find the slope of the line using these coordinates.
 
m = (48000 - 45000)/(2001 - 2009)
m = 3000/(-8)
m = -375
 
Equation is  y = -375x + b.   We must substitute values from any coordinate to find b.  Let's choose P₁.
 
45000 = -375(2009)+b
45000 = -753375+b
798375 = b
 
Your equation is
 
y = -375x + 798375