Page 322 - Algebra 1

L E S S O N Writing Equations in Slope-Intercept Form 49
Warm Up
1. Vocabulary Which ordered pair could be the coordinates of the (35) y-intercept of a graph?
A (3, 0) Solve for y.
2. x+3y-4=0 (29)
B
(0, 4)
C (1, 2) 3.3x-2y-7=0
(29)
5. y=x2;x=-9 (30)
D (-1, -6)
Find the y-value given the x-value. 4.y=2x+10;x=4
(30)
New Concepts The slope-intercept form of a linear equation can be used to graph lines quickly because it gives information about the characteristics of the graph of
the equation.
Determining the Slope and y-Intercept of a Line Determine the slope and the y-intercept of each equation.
a. y=3x-4
SOLUTION The equation is already written in slope-intercept form. The slope (m) is the coefficient of x, and the y-intercept is the constant value in the equation. Write the equation so that the operation with the constant is addition.
y = 3x + (-4)
slope: 3 y-intercept: -4
b. 2x+3y-9=0
SOLUTION Isolate the variable y to write the equation in slope-intercept form.
Slope-Intercept Form of an Equation
The slope-intercept form is y = mx + b, where the value of m is the slope of the line and the value of b is the y-intercept.
Math Language
The y-intercept is the y-value where a graph intersects the y-axis, and is usually represented by the variable b. The coordinate is (0, b).
Example
1
Online Connection www.SaxonMathResources.com
slope: -_2 3
y = - _2 x + 3 3
y-intercept: 3
2x + 3y - 9 = 0
-_ 2 _ x
-_ 2 _ x 3y - 9 = -2x
Subtraction Property of Equality
Addition Property of Equality Division Property of Equality
+_ _9 +_ _9 3y = -2x + 9
__ 33
Lesson 49 307