# Straight line function: depreciation after 1.5 years

#### bee2175

##### New member
The question is:
A company purchased a machine for 80,000, and they would like to use it for 5 years.
Show, using the straight line function, the depreciation of the machine over 5 years.
What would the depreciation of the machine be after 1 1/2 years?

I am afraid that I do not even know how to start this problem, and there are no examples in my text book.
I can picture the graph of this function as a straight line starting high on the y-axis and decreasing as x gets larger.
But, I do not know how to express this as a straight line function.

How do I begin?

#### Loren

##### Senior Member
Re: Straight line function

If I understand the problem correctly, if you plot the straight-line function with the y-axis being the value of the machine and the x-axis being the number of years the line would start at (0,80000) and end at (5,0). With that in mind you could write the equation of the line in the form $$\displaystyle y-y_1=\frac{y_2-y_1}{x_2-x_1}x-x_1$$ and go from there. If you don't like that form of the equation use y=mx-b where m is the slope and b is the y intercept.

#### Denis

##### Senior Member
Re: Straight line function

It's as simple as 80000/5 = 16000 per year.