SOL 
A.6a The student will graph linear equations and linear inequalities in two variables, including determining the slope of a line when given an equation of the line, the graph of the line, or two points on the line. Slope will be described as rate of change and will be positive, negative, zero, or undefined.

Concept of Slope
The following construction shows a line that runs through the origin of
the coordinate system and a moveable point M.
On the left, you can also see the corresponding linear equation.
Click to view the Geogebra lesson 
Practice with Slope
To move the red line you may click on and move Points A and B. Stop each point at an intersection point on the grid. Slope is the ratio of the vertical change to the horizontal change between two points.

Finding Slope Given 2 Points
To move the red line click on point A or B and use the up and down arrow keys.

