Journal Entry Equation of a Line

May 1, 2014

Slope

Slope is a measure of the steepness of a line. Slope is calculated as .

Remember rise is the vertical change (change in y) and run is the horizontal change (change in x).

run

rise

The slope of this line would be:

3

4

Important Points about Slope

A positive slope means that the line slopes upward, from left to right. It is increasing.

A negative slopes means that the lines slopes downward, from left to right. It is decreasing.

If I choose many different points on the same line, the slope connecting any two of the points will ALWAYS be the same.

If two different lines have the same slope, they are parallel.

Y-intercept

The y-intercept is the y-coordinate of the point where a line crosses the y-axis.

The y-intercept of this line is 1.

Important Points about the Y-intercept. When many different

lines have the same y-intercept, they will all cross at this point. It is called the intersection point of the lines.

Equation of a line

Remember that m is the slope and b is the y-intercept!!

Graphing a line from the equation Remember any equation will be in the form of

y=mx+b and m is always slope and b is always the y-intercept.

First I plot the y-intercept (the point on the y-axis), then I apply the slope (the rise and the run).

Example:Graph y= 2x + 4SOm = 2b=4

Finding the equation of a line

Now I have to read the values of the graph. Find the y-intercept (point that the line crosses the y-axis), this is the b. Then I find the slope (calculate the rise and the run), this is m. Now I just write the equation (y=mx+b).

Horizontal Line

Any horizontal line will have a slope of zero.

The equation of the line will be y=b (or y = y-intercept).

Vertical Line

Any vertical line will have no y-intercept (it doesn’t cross the y-axis) and the slope will be undefined.

Since there is no slope or y-intercept I can’t use y=mx+b.

The equation of the line will be x=x-intercept (point where line crosses the x-axis.