Page 344 - Algebra 1

L E S S O N Determining the Equation of a Line
52
Given Two Points
Warm Up
New Concepts
1. Vocabulary The is a measure of the steepness of a line. (41)
2. Find the x-intercept in the equation 3x + y = 6. (35)
3. Find the y-intercept in the equation 3x + y = 6. (35)
Solve each proportion. 4. _2 = _4
(36) 9 n
_
x + 10
5.
(36)
5 _1
=
3
A line can be graphed if the slope and any point
on the line are known. For example, to graph a
line that has a slope of -_2 and passes through 3
(2, 4), begin by plotting the point (2, 4). From the point (2, 4), count down two units and to the right three units. Plot a point there. Then draw
a line through the two points (2, 4) and (5, 2).
-2
4
-2
-4
Example
1
Hint
A slope of 4 is the same as _4 .
1
8
y
(4, 9)
6
(3, 5)
4
2
Math Language
The slope of a line represents a rate of change. A positive slope slants up to the right.
A negative slope slants down to the right.
x
2
4
6
8
y
4
(2, 3)
2
O
x
Online Connection www.SaxonMathResources.com
Using Slope and a Point to Graph
a. Graph a line that has a slope of 4 and passes through point (3, 5). SOLUTION
Graph the point (3, 5).
From the point (3, 5), count up four units and
to the right one unit. Graph a point there. Sketch the line through the two points (3, 5)
and (4, 9).
b. Graph a line that has a slope of 0 and passes through point (2, 3). SOLUTION
Graph the point (2, 3).
A line with a slope of 0 is a horizontal line.
Sketch a horizontal line that passes through the point (2, 3).
-4
-2
y
(2, 4)
4
2
O
2
(5, 2)
4
x
-4
2
-2
-4
Lesson 52 329