WRITE EQUATIONS TO SOLVE PROBLEMS
Many real-world situations
can be modeled using linear equations. In many business applications, the slope
represents a rate.
Write Linear Equations
CELL PHONE COSTS
Martina’s current cellular phone plan charges $14.95
per month and $0.10 per minute of air time.
a. Write an equation to represent the total monthly cost C for t minutes of
For each minute of air time, the cost increases $0.10. So, the rate of change, or
slope, is 0.10. The y-intercept is located where 0 minutes of air time are used,
The total monthly cost can be represented by the equation C
b. Compare her current plan to the plan presented at the beginning of the
lesson. If she uses an average of 40 minutes of air time each month, which
plan offers the better rate?
Evaluate each equation for t
Alternate plan: C
Given her average usage, Martina’s current plan offers the better rate.
1. Explain how you would write an equation of a line whose slope is
contains ( 2, 8).
2. Write equations in slope-intercept form for two lines that contain ( 1,
Graph a line that is not horizontal or vertical on the coordinate
plane. Write the equation of the line.
Write an equation in slope-intercept form of the line having the given slope and
GUIDED PRACTICE KEY
intercept at (0,
Write an equation in point-slope form of the line having the given slope that
contains the given point.
3, (7, 5)
1.25, (20, 137.5)
Lesson 3-4 Equations of Lines 147