In this lesson we will learn how to write the equation
of a line after we have been given the slope and y-intercept
of that line.

First, we need to introduce the slope-intercept formula:
y = mx + b
In this formula, "m" is the slope of the line,
and "b" is the y-intercept.

For example in the equation;
y = 3x +6
m = 3, so the slope is 3
b = +6, so the y-intercept is +6

Let's look at another:
y = 4/5x - 7
m = 4/5, so the slope is 4/5
b = -7, so the y-intercept is -7

Please note that in the slope-intercept formula;
y = mx + b,
the "y" term is all by itself on the left side of the equation. 
That is very important!
If the "y" is not all by itself, then we must first use
the rules of algebra to isolate the "y" term.
For example in the equation:
2y = 8x + 10
You will notice that in order to get "y" all by itself
we have to divide all of the terms by 2.
After you have done that, the equation becomes:
y = 4x + 5
Only then can we determine the slope (4), and
the y-intercept (+5).

Ok....so let's get back to the lesson....
Our job is to write the equation of a line after we
have been given the slope and y-intercept....

Let's try one..
Given "m" (the slope remember!) = 2
and "b" (the y-intercept) = +9
All we have to do is plug those values into
y = mx + b
The equation becomes..
y = 2x + 9

And another example....
Given m = 2/3, b = -12
Substitute those values into the formula
y = mx + b
y = 2/3x - 12

One last example...
Given m = -5, b = -1
Substitute those values into the formula
y = mx + b
y = -5x -1

As you can see, if you have been given the slope and y-intercept
all you have to do is plug those values into the formula
and you are done!  Easy!

For practice on your own...

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