Objectives
Graph data and use a trend line to
make predictions.
Understand how transformations
affect the look of an absolute value
graph.
Scatter Plots
Graphs that relate two different sets of data by plotting the data
as ordered pairs. Used to determine the relationship between data
sets (for example, x and y values).
Trend line: a line that approximates the relationship between the
data sets of a scatter plot. Used to make predictions.
Trend Lines by Hand
Graph the set of data. Decide whether a linear model is reasonable. If so,
draw a trend line and write its equation by hand. Then use a graphing
utility to determine the equation of the trend line.
{(1, 2), (3, 3), (3, 3.75), (4, 4), (5, 3.25), (6, 4.5)}
1. Place the ruler in such a way that
half of the points are above the
line and half of the points are
below.
2. Draw the line
3. Write an equation for the line
using two points
This is much less accurate than
calculator!
Trend Lines on a Calculator
Use a calculator to graph the set of data. Decide whether a linear model
is reasonable. If so, make a trend line and find its equation.
{(1, 2), (3, 3), (3, 3.75), (4, 4), (5, 3.25), (6, 4.5)}
1. Turn plots on:
- 2nd  STAT PLOT
- Select option 1
- Highlight the word “ON,” hit ENTER
2. Enter data into a list (L1 = x values, L2 = y values):
- STAT  option 1 (Edit) 
- Highlight the titles L1 and L2 and push CLEAR
- Enter your data into each list
3. GRAPH
- To show a reasonable domain and range hit ZOOM  9
Trend Lines on a Calculator cont.
4. Use the graph to determine if the data is linear. If so, find the
equation of the trend line:
- 2nd QUIT to be on a blank screen
- STAT  arrow over to CALC  option 4 (LinReg)  ENTER
- Write down your equation y = ax + b
5. Graph the trend line:
- Hit the Y= button. Clear all existing equations.
- VARS  option 5 (Statistics)  EQ  option 1 (RegEQ)
- GRAPH (ZOOM 9)
Trend Lines on a Calculator
An art expert visited a gallery and jotted down her guesses for the selling
price of five different paintings. Then she checked the actual prices. The
data points represent the cost (guess, actual) in hundreds of dollars.
{(1, 2), (3, 3), (3, 3.75), (4, 4), (5, 3.25), (6, 4.5)}
1. Will a linear model fit this data?
2. If so what is the equation of the trend line?
3. If the actual price of a 6th painting was $1600, what might have the
art expert’s guess been?
Homework #14:
Pg 81 #8, 12, 13, 21 (one of these
problems must be done by hand)
Pg 91 #29-32
2.1 – 2.4 QUIZ
DUE FRIDAY!!