Learning Resources

Investigation 3: Parallel and Perpendicular Lines

Step A

Remember that to plot a point whose coordinates are given, the first coordinate is the x-coordinate and is measured right or left, the second is the y-coordinate and is measured up or down. Thus to plot the point (3 , -4), we go 3 units to the right of the origin and 4 units down.

Step B

The formula for calculating the slope is in you text on page 222.  The subscripts are used to distinguish between the two points. Thus x₁ refers to the x-coordinate of the first point, and x₂ to the x-coordinate of the second point. The example below shows how to use it:

Find the slope of the segment joining (-3 , 5) and (2, -4).