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Unit 2 - Lesson 11 - Grade 8: Illustrative Mathematics

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Grade 8 Unit 2
Lesson 11: Writing Equations for Lines
CC BY 2021 Illustrative Mathematics®
Grade 8 Unit 2
Lesson 11: Writing Equations for Lines
CC BY 2021 Illustrative Mathematics®
Lesson: Writing Equations for Lines

Coordinates and Lengths in the Coordinate Plane (Warm Up)

Find each of the following.
1.

The length of segment BE. Explain your reasoning.

2.

The coordinates of E. Explain your reasoning.

What We Mean by an Equation of a Line

Line j is shown in the coordinate plane.
3.

What are the coordinates of B and D?

4.

Is point (20, 15) on line j? Explain how you know.

5.

Is point (100, 75) on line j? Explain how you know.

6.

Is point (90, 68) on line j? Explain how you know.

7.

Suppose you know the x- and y-coordinates of a point. Write a rule that would allow you to test whether the point is on line j.

Writing Relationships from Slope Triangles

8.

Complete the diagram so that all vertical and horizontal segments have
expressions for their lengths.

9.

Use what you know about similar triangles to find an equation for the quotient of the vertical and horizontal
side lengths of ΔDFE in each diagram.

10.

Complete the diagram so that all vertical and horizontal segments have
expressions for their lengths.

11.

Use what you know about similar triangles to find an equation for the quotient of the vertical and horizontal
side lengths of ΔDFE in each diagram.

Cool Down: Matching Relationships to Graphs

Matching Relationships to Graphs

12.

Explain why the slope a of line is 2/6.

13.

Label the horizontal and vertical sides of the triangle with expressions representing their length.

14.

Explain why...