1. 4-2 Writing Linear Equations Given Two Points
Goal:
Write the equation of a line in slope-intercept form given 2 points on the line.
Eligible Content:
A / A / A / A / A / A / A

2. Steps: Find the slope using the slope formula:
Find the y-intercept using y = mx + b
Write equation by plugging slope and y-intercept into y = mx + b.

3. Find the equation of the line that passes through the points (1,6) and (3, -4).
Slope: y-intercept: pick either point 6 = -5 ‧ 1 + b 6 = b = b Write equation: y = –5x + 11
If I pick the other point, I will get the same answer:
-4 = -5 ‧ 3 + b
-4 = b
11 = b

4. Examples
Write the equation of the line that goes through each set of points.
(-3, 1) and (5, 5)
(2, 3) and (3, 0)
(-4, -3) and (2, 9)
y = ½ x + 2.5
y = – 3x + 9
y = 2x +5

5. The table of ordered pairs shows the coordinates of two points on the graph of a line. Which equation describes the line?
A. y = –x + 4
B. y = x + 4
C. y = x – 4
D. y = –x – 4

6. Write the equation of the line that passes through the points (–2, –1) and (3, 14).
A. y = 3x + 4
B. y = 5x + 3
C. y = 3x – 5
D. y = 3x + 5

7. Practice
Page 229 #5-8

8. Homework
Page 229 #16-21