4-1 Writing Linear Equations in Slope-Intercept Form Goals: Use the slope and y-intercept to write the equation of a line. Model a real-life situation with a linear equation. Eligible Content: A1.1.2.1.1 / A1.1.2.1.3 / A1.2.1.1.1 / A1.2.1.2.1 / A1.2.1.2.2 / A1.2.2.1.3 / A1.2.2.1.4

Example Write the equation of the line whose slope is -2 and whose y-intercept is 5. y = mx + b y = x + y = -2x + 5 m b -2 5

Examples Write an equation in slope-intercept form. Slope is 3, y-intercept is -5 y = 3x – 5 m = -3, b = 6 y = -3x + 6 Slope is – ½, y-intercept is -4 y = - ½ x – 4

Write an equation in slope-intercept form of the line whose slope is 4 and whose y-intercept is 3. A. y = 3x + 4 B. y = 4x + 3 C. y = 4x D. y = 4

Write the equation of each graph. 1. 2.

Example #3 Which of the following is an equation in slope-intercept form for the line shown in the graph? A. B. C. D.

Which of the following is an equation in slope-intercept form for the line shown in the graph? B. C. D.

Practice Write an equation in slope-intercept form. m = 5, b = 8 Slope is 6, y-intercept is – 3 b = 4, m = ¼ y-intercept is 2, slope is -6 m = 1, b = 0 y = 5x + 8 y = 6x – 3 y = ¼ x + 4 y = -6x + 2 y = x

Word Problems Slope is rate of change!!! Look for words like per, for each, for every… y-intercept is the beginning amount Look for words like beginning, initial…

Word Problem #1 Your family decides to rent bikes while you are on vacation. It costs $4 to rent the bike, plus $1.50 per hour. Write an equation in slope-intercept form that models this situation. y = 1.5x + 4 How much will it cost to rent the bike for 12 hours? $22

Word Problem #2 In 1990, the population in California was 29.76 million. During the next 25 years, the population increased by .31 million people per year. Write an equation in slope-intercept form that models this situation. y = .31x + 29.76 How many people were there in California in 2005? 34.41 million people

Word Problem #3 A telephone call costs $3.44 for the first minute, and $.24 for each additional minute. Write an equation in slope-intercept form that models this situation. y = .24x + 3.44 How much will it cost for a 9 minute phone call? $5.36

The amount of money spent on Christmas gifts has increased by an average of $150,000 ($0.15 million) per year since 1986. Consumers spent $3 million in 1986. Write a linear equation to find the average amount D spent for any year n since 1986. A. D = 0.15n B. D = 0.15n + 3 C. D = 3n D. D = 3n + 0.15

The amount of money spent on Christmas gifts has increased by an average of $150,000 ($0.15 million) per year since 1986. Consumers spent $3 million in 1986. Find the amount spent by consumers in 1999. A. $5 million B. $3 million C. $4.95 million D. $3.5 million

Homework Pages 220-221 #11-22 #37, 50,51 You do not have to graph any equations!