What is the equation of the following line
(0,0) and (10,-2)

Okay, the first step to answering this probelm is finding the slope of this line. 
The equation for slope is 
y₂-y₁

x₂-x₁
Plug the points in 
-2 - 0       -2              1
= = -   (negative 1/5) 
10 - 0       10             5
 Now we will use the point slope equation 
y - y₁ = m(x- x₁)
Lets use the point (10,-2)
Plug in the x,y, and your new slope- then simplify 
y +2 = -1/5(x -10)
y + 2 = -1/5x + 2
y = -1/5x 

That's your final equation!

Hope this ; )