The easiest way to show you how to do this is by working out an
Example: Find the equation of the line joining
The first thing we do is find the slope. To do that you have to know
how to subtract integers.
Remember that the slope is rise over run
which is the same thing as saying the change in y over the change in x.
If we use the formula y = mx + b, where
m is the slope and
b is the y-intercept, we get
Of course, if we had done it the other way, we would have ended up
with the same answer.
So, now our equation is:
Now we have to solve for the y-intercept. We do that by picking one
of our points, and plugging the values into the equation. Let's do it
with (-2, 8):
As you can see, it helps to know how to
multiply a fraction and a whole number
and subtract a fraction from a
So, our final equation is:
If you're not a big fan of fractions, you can
multiply both sides of the equation by 5 to
get 5y = 13x + 66. If you want the
variables on one side and the y-intercept on the other, we would have
5y - 13x = 66 which is the form the
equation is usually written in when we are solving for the intersection
point of 2 lines.