1. 3-4 Equations of Lines
Name the slope and y-intercept of each equation.
1. y = ½ x + 4
m = ½ b = 4
2. y = 2
m = 0, b = 2 (horizontal line)
3. x = 5
m = undefined, no y-intercept (vertical line)
4. 4x – 3y = 12
Put into y = mx + b form
y = 4/3 x – 4; m = 4/3, b = -4
Linear equation: Equation of a line
Slope-intercept Form: y = mx + b
m = slope of line
b = y-intercept (where the line crosses the y-axis)

2. Graph using slope-intercept form
Graph 2x – y = 4
First put it into the correct form.
y = 2x – 4
What is m? What is b?
m = 2
b = -4
Graph the y-intercept first.
Then from that point use the slope to get your second point.
Connect the dots.

3. Your Turn
Graph the line –x + 3y = 9

4. Writing Equations
Write an equation of the line that is parallel to the line y = -2x + 3 and passes through the point at (0,1).
1. What is the slope of the line given? -2
2. What is the slope of the line parallel to that?
Plug in the slope, the x and y from the given point to find b.
y = mx + b
1 = (-2)(0) + b
1 = 0 + b
1 = b
Now plug b and m into slope-intercept form, leaving x and y as variables.
y = -2x + 1
Use the point-slope form: y – y1 = m(x – x1)
y – 1 = -2(x – 0)
y – 1 = -2x

5. Point – Slope form of a line
y – y1 = m(x – x1)
m = slope
x1 and y1 is the given point
Write and equation in point-slope form with slope 4 that contains (-3,-6). Then simplify and write the equation in slope-intercept form.
y + 6 = 4(x + 3)
y = 4x + 6

6. Your Turn
Write an equation of the line perpendicular to the graph of y = 3x + 4 that passes through the point (6,9).
Slope = 3 so the perpendicular slope = -1/3
Point (6,9) so x1 = 6 and y1 = 9
Using point-slope form y – y1 = m(x – x1), write the equation of the line.
y = -1/3x + 11

7. Practice
Homework #21 p odd, 33-34, 46-47