Parallel Lines

Slope and Parallelism

​Why is this relevant?

Geometry is the study of physical space (both 2 dimensional and 3 dimensional). We can use coordinate geometry to help us map and plan in 2D before bringing plans to life in 3D

Open Ended

In what real life scenarios would it be important to create something in 2 dimensions before constructing in 3 dimensions?

Two line segments AB and CD are shown graphed to the left. Determine the slope of both of these lines graphically. Recall that slope is the ratio of the rise to the run as we move from left to right.

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​Exercise 1

Multiple Choice

The slope (Change in y / Change in x) is

• -1/2

• 2

• -2

• 1/2

Poll

Before finding the slope of CD should it be positive or negative?

• Positive

• Negative

Open Ended

What is the slope of CD?

Draw

How can we show on the graph the slope of AB?

If (x1, y1) and (x2,y2) represent the endpoints of a line segments (or any two points on a line), then

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Slope Formula

Draw

Show the substitution to calculate the slope of CD.

Multiple Choice

What is the slope of EF?

• Error

• 1/2

• 0

• 2

Draw

Find the slopes of all 4 lines on the graph provided.

Two non-vertical lines will be parallel if and only if they have slopes that are equal.

Open Ended

Are the lines AB and CD parallel? Why?

Open Ended

Are AC and BD Parallel? How do you know?