WRITING AN EQUATION OF A LINE

Lesson Five

Part One

WARM UPToday’s warm up is a Scavenger Hunt. You and your partner will have ten minutes to complete this activity. You may start at ANY work card/station. You will need to find the SLOPE of the lines. Work carefully, it’s for a grade.

Today we are going to write the equation of a line using a table, graph and values for m and b.

m = slope

y = y-intercept

What have you learnt so far…..• You can find the slope of a line from a table.

• You can find the slope of a line from two points using the formula:

(-3, 6) and (4, 5) m = = =

• You can find the slope of a line from a graph.

m = - = -1

Time 3 6 9 12

Money $15 $30 $45 $60

Slope intercept form……

y = mx + b

slope y-intercept

Writing the equation from a graph…. From the graph, you can see that the slope is m = and the y-intercept is b = –2. Use slope-intercept form to write an equation of the line.

y = mx + b Use slope-intercept form.

y = x + (–2)34

Substitute for m and –2 for b.3

4

y = x – 2 Simplify.

Now you try. Find the equation of the line.

• What should you do first?

• What should you do second?

• What is your answer?

Write an equation of the line that has the given slope and y-intercept.

1. m = 3, b = 1

y = 3x + 1ANSWER

2. m = –2 , b = –4

y = –2x – 4ANSWER

y = – x +34

72

ANSWER

Writing equations given slope (m) and y-intercept (b)...

3. m = -

y = mx + b

slope y-intercept

Now you try. Write the equation of the line given the slope and the y-intercept.

a. slope: 2; y-intercept: -6

b. slope: ½; y-intercept: 3

c. slope: -1; y-intercept: -6

Writing equations from tables...X Y

0 5

2 12

4 19

6 26

8 33

• What is the slope of the table? (find the change in y over the change in x: )

• What is the y-intercept? (look for the point where x = 0 and y = some number. Y-int = 5, line cuts the graph at y = 5)

• Substitute into your equation: y = mx + b. (y = )

Now you try….find the equation of the line from the table.

0 4 81216

–3 0 3 6 9

x y

CLASSWORK

Answer # 1 – 9 on the blue sheet. Check your answer. If you have everything correct, you may move on to the next station.

Answer #s 10 – 15 on the green sheet. Check your answers. If you have all six correct, move on to the next station.

Answer #s 16 – 20 on the yellow sheet. Check your answers. If all your answers are correct, turn you work in to be graded.

HOMEWORKComplete the following pages from your workbook: