C. Horizontal and Vertical Lines

C. Horizontal and Vertical Lines

In this lesson, you've been introduced to the general form of a linear equation, but why use it? The slope-intercept form is easier to interpret and easier to enter into many graphing programs.

One reason to use the general form is that the slope-intercept form cannot be used to represent all linear relations. The following investigation explores this problem.

 

Investigation

1. The following graph shows three linear relations.
   
   
   
   

   1. Determine the slope of each line.
      
      
      
      

   2. Write the equation of each relation in slope-intercept form. Simplify the equations, if possible.
      
      
      
      

2. Describe a general rule for determining the equation of a horizontal line.
   
   
   
   
   
   

3. The following graph shows three linear relations.
   
   
   
   
   

   1. Determine the slope of each line.
      
      
      
      

   2. Write the equation of each relation in slope-intercept form. Simplify the equations, if possible.
      
      
      

   
   

4. Based on the rule you determined in part 2., suggest a general rule for writing the equation of a vertical line.