1. Application using calculator and algebra
A study has found that generally the height y of women in centimeters is given by
y – 3.9x = 73.5
where x is the length of the radius bone (from elbow to wrist) in centimeters.
Find the missing data:
Use
algebra
graphing calculator. x y
20cm
23cm
25cm
135cm
147cm

2. Solve equation for y ; express as y = ……….. y = 73.5 + 3.9x
Using TI-83 or 83+
y – 3.9x = 73.5
Solve equation for y ; express as y = ………..
y = x
2. Enter equation into calculator ……..
With a standard viewing window you see:….
ZOOM 6
Y =
WINDOW
GRAPH

3. …….choose an appropriate window.
To see the graph of y = x
…….choose an appropriate window.
1. Use algebra (e.g. sample points or intercepts), to predict graph position, or
2. Use Zoom features on calculator:….
ZoomFit option will choose a window for you, with a portion of your graph in it – use as guide.
ZOOM
WINDOW

4. Choose a more suitable window for this specific problem
Choose a more suitable window for this specific problem. Negative x or y values are irrelevant for heights and lengths. For example, you might choose one of the following:….
Note: graph is same in both cases, but the viewing window is different.

5. Use Trace feature to approximate y when x=23cm
Use arrow keys to move cursor along line – watch bottom line values
under estimate for x
over estimate for x
Or press x key
then backspace and enter exact value for x

6. Table features: set table and view values in a table
TBL SET
Choose
starting value
increment
2nd
TABLE
To view entries, use arrow keys to scroll up or down.

7. Found missing data…… x y
20cm
23cm
25cm
135cm
147cm
151.5cm
163.5cm
171cm
Need different strategy to find x-values for given y-values using the calculator

8. Use Trace feature to approximate x when y=135cm
Use arrow keys to move cursor along line.
Watch bottom line for best estimate of required values.
under estimate for y
over estimate for y

9. More accurate method to find x when y=135cm
Enter a second linear equation
y = 135
Y =
GRAPH
Point of interest
y = 135
x-value corresponding to y = 135

10. More accurate method to find x when y=135cm
Use calculate feature
to find co-ordinates of the intersection
( x , 135)
y = 135
2nd
CALC
Choose option 5 5

11. Calculate feature continued…..
y = 135
ENTER
ENTER
Move cursor close to point of interest
Answer
ENTER

12. Found missing data…… x y
20cm
151.5cm
23cm
163.5cm
25cm
171cm
135cm
147cm
y = 135
~15.8cm

13. Similarly for y = 147cm…… x y
20cm
151.5cm
23cm
163.5cm
25cm
171cm
135cm
147cm
y = 147
~15.8cm
~ 18.8cm