What is an equation of the line that passes through the points (1,2) and (2,-1) 

You should also try solving it yourself to make sure I did not make any mistake.

Step-by-step explanation:

Equation

First we need to know the slope

So far the equation will look like this

To get the b you insert a point into the equation like this. I picked point (1,2)

We could also check it with the other point and see if we get the same answer.

So the equation is