Applying Similar Triangles to Finding the Slope of a LInear Equation Concluded

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SWBAT see different connections between similar triangles and the slope of a linear equation through differentiated tasks.

Big Idea

Students take ownership and bring their 8th grade year full circle then present their ideas to the class.

Lesson Opening

10 minutes

Clarify the intentions of the lesson again.  Tell students that in 10 minutes each group will be called to the board to present at least two connections they have made between similar triangles and the slope of a linear equation.  If groups are struggling to understand possible connections, I encourage them to look at question 3 to get ideas as this is individualized for each group.  I allow 10 minutes to complete the group work and I move about the room assessing learning, providing feedback, and discussing with each group which ideas they will present to ensure I get variety and I know in which order to pull groups to the board.  Click on the video resource below to watch a clip on how to apply these strategies in the classroom.

-Clarifying and sharing learning intentions

-Grouping Students

-Activating students as resources for one another

-Providing feedback that moves learning forward

-Activating students as owners of their own learning

Group Presentations

45 minutes

Standards Addressed

1 minutes

This activity applies similar triangles to finding the slope of a linear equation using any two points along the line.  Different groups are meant to make different connections to this main idea but the overall math standard addressed is 8.EE.B.6 Use similar triangles to explain why the slope m is the same between any two distinct points on a non-vertical line in the coordinate plane; derive the equation y = mx for a line through the origin and the equation y = mx + b for a line intercepting the vertical axis at b.


The math practice standards used throughout this activity arise from students working in cooperative groups to determine how similar triangles apply to slope of a linear equation and then decide which two connections to present to the rest of the class.  Working throughout the activity to make difficult connections addresses practice standard MP1 Make sense of problems and persevere in solving them. Group discussion addresses standard MP3 Construct viable arguments and critique the reasoning of others.  Working with similar triangles to see slope and make connections brings in standard  MP7 Look for and make use of structure.  Using coordinates to graph and find distance to the nearest hundredth bring in accuracy and address standard MP6 Attend to precision.  One goal of this activity is that every group will understand why students who graph linear equations fluently use the concept rise/run to graph additional points past the y-intercept.  By looking at this structure of similar triangles, the pattern of consistent rise/run should become obvious and this structure is really applying practice standard MP8 Look for and express regularity in repeated reasoning.