Using Two Variables
8-2Points, Lines, and Their Graphs
Overview
Plot ordered pairs in the coordinate plane. The graph of an equation is the set of all its solution points.
Key ideas
- x-axis is horizontal, y-axis is vertical.
- Quadrants are numbered I–IV counterclockwise.
- Two points determine a line.
Worked examples
Example 1
Problem. Plot (3, −2).
Solution. Go right 3, down 2.
Example 2
Problem. Graph y = x + 1 by plotting two points.
Solution. (0, 1) and (1, 2); draw line through them.
Practice
Try each one. Click Show answer when ready.
- 1.
Which quadrant: (−4, 5)?
- 2.
Which quadrant: (2, −3)?
- 3.
Name two points on y = 2x.
Challenge problems
A little tougher — great for test prep. Click Show answer when ready.
- 1.
Graph the line through (2, 3) and (−1, −3). Find the slope.
- 2.
Where does the line 2x + 3y = 6 cross the x-axis and y-axis?