1. 3-4 Day 1 Equations of Lines

2. 2 Forms

3. Example
Write an equation in slope-intercept form of the line with slope of 6 and y-intercept of –3. Then graph the line.
y = mx + b Slope-intercept form
y = 6x + (–3) m = 6, b = –3
y = 6x – Simplify.

4. Example Answer: Plot a point at the y-intercept, –3.
Use the slope of 6 or to find another point 6 units up and 1 unit right of the y-intercept.
RISE OVER RUN!!!
Draw a line through these two points.

5. Example
Write an equation in slope-intercept form of the line with slope of –1 and y-intercept of 4.
A. x + y = 4
B. y = x – 4
C. y = –x – 4
D. y = –x + 4

6. Example
Write an equation in point-slope form of the line whose slope is that contains (–10, 8). Then graph the line.
Point-slope form
Simplify.

7. Example Answer: Graph the given point (–10, 8).
Use the slope to find another point 3 units down and 5 units to the right.
Draw a line through these two points.

8. Example
Write an equation in point-slope form of the line whose slope is that contains (6, –3). A. B. C. D.

9. Example
Given Two Points
Write an equation in slope-intercept form for a line containing (4, 9) and (–2, 0).
Step 1 First, find the slope of the line.
Slope formula
x1 = 4, x2 = –2, y1 = 9, y2 = 0
Simplify.

10. Example
Step 2 Now use the point-slope form and either point to write an equation.
Point-slope form
Using (4, 9):
Distributive Property
Add 9 to each side.
Answer:

11. TWAP!!
Write an equation in slope-intercept form for a line containing (–3, –7) and (–1, 3).
Slope
Using (–1, 3):
Add 3 to each side.
y = 5x + 8
Answer:

12. SPECIAL LINES!! y = a #, Horizontal line, slope = 0 x = a #, Vertical line, slope = Undefined

13. Example
What do we notice about the ordered pairs and our answer???
Write an equation of the line through (5, –2) and (0, –2) in slope-intercept form.
Step 1
This is a horizontal line.
Answer:

14. TOO:
Find an equation for (3, -2) and (3, 5) WITHOUT finding slope!!
Answer: x = 3

15. HW: Pg. 202-203 #13-35 ODD Graphs for #13-23