Lesson 12Using Equations for Lines
Learning Goal
Let’s write equations for lines.
Learning Targets
I can find an equation for a line and use that to decide which points are on that line.
Lesson Terms
- similar
- slope
Warm Up: Missing Center
Problem 1
A dilation with scale factor 2 sends
Activity 1: Writing Relationships from Two Points
Problem 1
Here is a line.
Using what you know about similar triangles, find an equation for the line in the diagram.
What is the slope of this line? Does it appear in your equation?
Is
also on the line? How do you know? Is
also on the line?
Are you ready for more?
Problem 1
There are many different ways to write down an equation for a line like the one in the problem. Does
Activity 2: Dilations and Slope Triangles
Problem 1
Here is triangle
. Draw the dilation of triangle
with center and scale factor 2. Draw the dilation of triangle
with center and scale factor 2.5.
Where is
mapped by the dilation with center and scale factor ? For which scale factor does the dilation with center
send to ? Explain how you know.
Lesson Summary
We can use what we know about slope to decide if a point lies on a line. Here is a line with a few points labeled.
The slope triangle with vertices