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Graphing Calculator Activity for use with Lesson 10.3
ACTIVITY 10.3
Using Technology
Graphing Circles
When you use a graphing calculator to draw a circle, you need to remember
two things. First, most graphing calculators cannot directly graph equations
such as x 2 + y 2 = 36 because they are not functions. Second, to obtain a graph
with true perspective (in which a circle looks like a circle) you must use a
“square setting.”
EXAMPLE
Use a graphing calculator to draw the graph of x2 + y2 = 36.
SOLUTION
1 Begin by solving the equation for y.
2
2
x + y = 36
y2 = 36 º x2
y = ±36
ºx2
Y1= (36-X2)
Y2=- (36-X2)
Y3=
Y4 =
Y5 =
Y6 =
Y7 =
Enter the two equations into the graphing calculator.
INT
STUDENT HELP
NE
ER T
KEYSTROKE
HELP
See keystrokes for
several models of
calculators at
www.mcdougallittell.com
2 Next set the viewing window so that it has a “square
setting.” On some graphing calculators you can select
a square setting, such as “ZSquare.” On a graphing
calculator whose viewing window’s height is two
thirds its width, you can obtain a “square setting” by
choosing maximum and minimum values that satisfy
this equation:
RANGE
Xmin=-12
Xmax=12
Xscl=1
Ymin=-8
Ymax=8
Yscl=1
Ymax º Ymin
2
= Xmax º Xmin
3
3 The graph is shown at the right. (Some calculators
may not connect the ends of the two graphs.)
EXERCISES
Use a graphing calculator to graph the equation. Write the setting of the
viewing window that you used and verify that it is a square setting.
608
1. x2 + y2 = 121
2. x2 + y2 = 50
3. x2 + y2 = 484
4. 5x2 + 5y2 = 120
16
5. x2 + y2 = 9
1
1
6. x2 + y2 = 72
2
2
4
4
7. x2 + y2 = 20
5
5
8. 9x2 + 9y2 = 4
9. 125x2 + 125y2 = 1000
Chapter 10 Quadratic Relations and Conic Sections