standard_description: Use informal arguments to establish facts about the angle sum and exterior angle of triangles, about the angles created when parallel lines are cut by a transversal, and the angle-angle criterion for similarity of triangles. For example, arrange three copies of the same triangle so that the sum of the three angles appears to form a line, and give an argument in terms of transversals why this is so.
problem_activity: Warm-up
The purpose of this warm-up is for students to review plotting and labeling points that include negative coordinates and use repeated reasoning to generalize patterns in the coordinates of points in each quadrant (MP8).
Digital
Launch
Arrange students in groups of 4. Assign each person in a group a different quadrant. Tell students you will give them 2 minutes to plot and label at least three points in their assigned quadrant, and up to six if they have time. Give students 2 minute of quiet work time. Give students 4 minutes to share their points and their coordinates with their small group and look for patterns in the coordinates of points in each quadrant. Follow with whole-class discussion.
Though the paper and pencil version may be preferred, a digital applet is available for this activity.
Student Facing
Plot points in your assigned quadrant and label them with their coordinates.
Student Response
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for free access to Student Response.
Print
Launch
Arrange students in groups of 4. Assign each person in a group a different quadrant. Tell students you will give them 2 minutes to plot and label at least three points in their assigned quadrant, and up to six if they have time. Give students 2 minute of quiet work time. Give students 4 minutes to share their points and their coordinates with their small group and look for patterns in the coordinates of points in each quadrant. Follow with whole-class discussion.
Though the paper and pencil version may be preferred, a digital applet is available for this activity.
Student Facing
Plot points in your assigned quadrant and label them with their coordinates.
[IMG]
Student Response
Teachers with a valid work email address can
click here to register or sign in
for free access to Student Response.
Activity Synthesis
The focus of the discussion is for students to explain why the following patterns emerge:
In quadrants I and IV, the x-coordinate of a point (or the first number in an ordered pair) is positive.
In quadrants II and III, the x-coordinate of a point is negative.
In quadrants I and II, the y-coordinate of a point (or the second number in an ordered pair) is positive.
In quadrants III and IV, the y-coordinate of a point in is negative.
Ask the students to share any patterns they noticed among the coordinates of the points in each quadrant. After each student shares, ask the rest of the class if they noticed the same pattern within their small group. Record and display these patterns for all to see. If possible, plot and label a few example points in each quadrant based on students' observations.


aligns: no