#### Transcript Document

```Warm Up
1. Determine if this relation is a function.
2. Find π(3) if π π₯ =
π₯ 2 β2
.
π₯β1
3. Find the x-intercept and y-intercept of the graph of
3π₯ β 5π¦ = 15. The graph the equation.
4. Find the slope of a line that passes through (3, 5)
and (4, 1).
2.4 Writing Equations of Lines
The slope intercept form of the equation of
a line is π¦ = ππ₯ + π where π is the
___________ and π is the _____________.
Slope-Intercept Form
If you are given the slope and y-intercept
of a line, you can find an equation of the
line by substituting the values of π and π
into the slope-intercept form.
1. π ππππ
4
, πππ π ππ
3
π‘βπππ’πβ 0, 4
Examples
Sometimes it is necessary to calculate the
slope before you can write an equation.
Write an equation in slope-intercept form
for the line.
Write an equation of the line.
1. πππ π ππ  π‘βπππ’πβ 0, β6 πππ β4, 10 .
2. πππ π ππ  π‘βπππ’πβ 6, β2 π€ππ‘β π π ππππ ππ β 4.
Point-Slope Form
The point-slope form of the equation of a line is
π¦ β π¦1 = π(π₯ β π₯1 ), where (π₯1 , π¦1 ) are the
coordinates of a point on the line and π is the
slope of the line.
Using a previous example:
Write an equation of a line through 6, β2 with
a slope of 4 using point-slope form.
Write an equation of the line.
1. πππ π ππ  π‘βπππ’πβ 2, 3 π€ππ‘β π π ππππ ππ
1
2
2. πππ π ππ  π‘βπππ’πβ β2, β1 π€ππ‘β π π ππππ ππ β 3.
Standardized Testing
Tests like HSAP or the COMPASS love to ask questions
like thisβ¦
Which is an equation of the line that passes
through (-2, 7) and (3, -3)?
A. π =
π
π
π
β
π
π
B. π = βππ + π
C. π =
π
π
π
+π
D. π = ππ + ππ
Equations of a Line
What if you are asked to write the equation
of a line given two points?
(-8, -5) and (-3, 10)
What would you have to do?
1.
Find the SLOPE (π)
2.
Use point-slope form to find the equation
Parallel Lines
How do you know if two lines are parallel?
Their SLOPES are the SAME!
π¦ = 3π₯ β 1 and π¦ = 3π₯ + 13
π¦=
1
π₯
2
and π¦ =
1
π₯
2
+1
Example
Write an equation of a line that passes through
π
(12, 0) and is parallel to π = β π β π.
π
Write an equation of a line that passes through (0, 9)
π
and is parallel to π = π β ππ.
π
Perpendicular Lines
How do you know if two lines are perpendicular?
Their SLOPES are the NEGATIVE RECIPROCALS!
π¦ = 3π₯ β 1 and π¦ =
π¦ = β2π₯ and π¦ =
1
β π₯
3
1
π₯
2
+ 13
+1
Example
Write an equation of a line that passes through
π
(5, -6) and is perpendicular to π = β π + π.
π
Write an equation of a line that passes through
(6, -1) and is parallel to π = ππ β π.
Summary
Slope-Intercept Form:
Point-Slope Form:
Equations of a line: (1)
(2)
Parallel Lines:
Perpendicular Lines:
Homework!!! YAY! ο
Lesson 2.4
Page 87
#βs 9, 13, 15, 17-19, 23, 24 and 32
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