Big Ideas Math Integrated I, 2016
BI
Big Ideas Math Integrated I, 2016 View details
2. Writing Equations in Point-Slope Form
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Exercise 34 Page 176

Practice makes perfect
a

We have been given a table showing the cost for renting a beach house.

Days 2 4 6 8
Total Cost (dollars) 246 450 546 858
The situation can be modeled by a linear equation if the rate of change is constant. We can calculate the rate of change using the Slope Formula. m=y_2-y_1/x_2-x_1 Let's find the rate of change for the ordered pairs in the table.

(x_1,y_1), (x_2,y_2) y_2-y_1/x_2-x_1 m
( 2, 246), ( 4, 450) 450- 246/4- 2 102
( 4, 450), ( 6, 546) 546- 450/6- 4 102
( 6, 546), ( 8, 858) 858- 546/8- 6 102

We can see that the rate of change is constant. Therefore, the situation can be modeled by a linear equation.

b

To determine the processing fee and the daily fee, let's find the linear equation which models this situation. Recall the point-slope form of a linear equation.

y- y_1= m(x- x_1) Here m is the rate of change and ( x_1, y_1) is a point on the line. In Part A we already determined that the rate of change is 102. Let's substitute this and the point ( 2, 246) into the formula. y- y_1&= m(x- x_1) &⇓ y- 246&= 102(x- 2) To find the processing fee and the daily fee we need to rewrite this into slope-intercept form.

y-246=102(x-2)
y-246=102x-204
y=102x+42

We now have an equation which models the situation. y=102x+42 Now we know the daily fee is $102. The processing fee is $42, as this is a fixed amount that is paid only once no matter how many days the beach house is rented.

c

Since we can spend no more than $1200 on the beach house rental, the cost must be less than or equal to 1200. We can represent this as an inequality.

102x+42 ≤ 1200 Let's solve it!

102x+42 ≤ 1200
102x ≤ 1158
x≤ 1158/102
x ≤ 11.352941...
x ≤ 11.4

Since x is the number of days and we cannot rent the house for a fraction of a day, we can conclude that the maximum number of days we can rent the beach house is 11.