1. Sec 4.8: The x and y intercepts.
Objectives:
• Find the x- and y-intercepts of linear
equations.
• Use intercepts to graph the equation

2. What does it mean to INTERCEPT a pass in football?
The path of the defender crosses the path of the thrown football.
In algebra, what are x- and y-intercepts?

3. Concept: What are the x- and y-intercepts?
The x-intercept is where the graph crosses the x-axis. The y-coordinate is always 0. The y-intercept is where the graph crosses the y-axis. The x-coordinate is always 0.
(2, 0)
(0, 6)

4. So when is it a good idea to use x and y intercepts to graph???
Concept: When to Use Intercepts
So when is it a good idea to use x and y intercepts to graph???
When the two coefficients go into the constant!!
2x + 3y = ÷ 2 = and 6 ÷ 3 + 2
-3x – 4y = ÷ –3 = –8 and 24 ÷ –4 = –6
12x + 5y = ÷ 12 = 5 and 60 ÷ 5 = 12
5x – 4y = ÷ 5 = 8 and 40 ÷ –4 = 10
Notice: there are no fraction answers.

5. Concept: Finding The Intercepts
Plug in 0 for y – this is the x- intercept
Plug in 0 for x – this is the y- intercept

6. Concept: Finding The Intercepts cont…
Example #1: Find the x interecept. y x 5 -5
6x + 12y = 36
6x + 12(0) = 36
6x = 36
(6, 0) 6 6
x = 6

7. Concept: Finding The Intercepts cont…
Example #2: Find the y interecept. y x 5 -5
(0, 3)
-3x + 6y = 18
-3(0) + 6y = 18
6y = 18 6 6
y = 3

8. Concept: Finding The Intercepts cont…
2x + 3y = 6
2x + 3(0) = 6
2x = 6 y x 5 -5 2 2
x = 3
(0, 2)
2x + 3y = 6
(3, 0)
2(0) + 3y = 6
----- Meeting Notes (2/8/16 08:39) -----
3y = 6 3 3
y = 2

9. YOU TRY: Find the x- and y-intercepts. x – 2y = 12
Concept: Finding The Intercepts cont…
YOU TRY: Find the x- and y-intercepts x – 2y = 12
x-intercept: Plug in 0 for y.
x – 2(0) = 12
x = 12; (12, 0)
y-intercept: Plug in 0 for x.
0 – 2y = 12
y = -6; (0, -6)

10. Cover up method Concept: Short Cut x = 4 y = 2 Solve for x and y.
Hint: Cover up the 4y first.
Hint: Cover up the 2x this time.
Solve for x and y.
2x + 4y = 8
2x + 4y = 8
2x = 8 y x 5 -5
4y = 8
x = 4
y = 2

11. Additional Examples on board:
y = 3x + 9
y – 8 = 2(x – 2)

12. Homework
IXL: A1: S.12 PM 4.8