Big Ideas Math Algebra 1, 2015
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Big Ideas Math Algebra 1, 2015 View details
Chapter Review
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Exercise 5 Page 226

Start by using the Slope Formula to find the slope.

f(x)=-5/3x+18

Practice makes perfect
An equation in slope-intercept form follows a specific format. In this case, we are asked to write our equation in function notation. f(x)= mx+ b For an equation in this form, m is the slope and b is the y-intercept. We have also been given two points in function notation. To write these points as coordinate pairs, remember that the input x is the x-coordinate and the output f(x) is the y-coordinate. f( x)= y ⇔ ( x, y) f( 6)= 8 ⇔ ( 6, 8) f( 9)= 3 ⇔ ( 9, 3) Let's use the given points to calculate m and b. We will start by substituting the points into the Slope Formula.
m = y_2-y_1/x_2-x_1
m=3- 8/9- 6
â–Ľ
Simplify right-hand side
m=-5/3
m=-5/3
A slope of - 53 means that for every 3 horizontal steps in the positive direction, we take 5 vertical steps in the negative direction. Now that we know the slope, we can write a partial version of the equation. f(x)= -5/3 x+ b To complete the equation, we also need to determine the y-intercept, b. Since we know that the given points will satisfy the equation, we can substitute one of them into the equation to solve for b. Let's use ( 6, 8).
f(x)=-5/3x+b
8=-5/3( 6)+b
â–Ľ
Solve for b
8=-30/3+b
8=-10+b
18=b
b=18
A y-intercept of 18 means that the line crosses the y-axis at the point (0, 18). We can now complete the equation. f(x)= -5/3x+ 18