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EL-9900 Graphing Calculator
12-2
Solve the equation for y.
Enter y =
√
4 - x
2
for Y1 (the top
half). Enter y = -
√
4 - x
2
for Y2.
x
2
- 2x + y
2
+ 4y = 2
x
2
-2x+y
2
+4y+4=2+4
x
2
- 2x + (y+2)
2
= 6
(y+2)
2
= 6 -x
2
+ 2x
y+2 =
±
√
6-x
2
+2x
y =
±
√
6-x
2
+2x -2
Graphing Circles
The standard equation of a circle of radius r that is centered at a point (h, k) is (x - h)
2
+
(y - k)
2
= r
2
. In order to put an equation in standard form so that you can graph in rectangular
mode, it is necessary to solve the equation for y. You therefore need to use the process of
completing the square.
Graph the circles in rectangular mode. Solve the equation for y to put it in the
standard form.
Example
1. Graph x
2
+ y
2
= 4.
2. Graph x
2
- 2x + y
2
+ 4y = 2.
1-1
2-1
Solve the equation for y,
completing the square.
Place all variable terms on the
left and the constant term on
the right-hand side of the
equation.
Complete the square on the
y-term.
Express the terms in y as a
perfect square.
Leave only the term involving
y on the left hand side.
Take the square root of both
sides.
Solve for y.
y
2
= 4 - x
2
y =
√
4 - x
2
1-2
View the graph.
This is a circle of radius r ,
centered at the origin.
ENTERENTER
1
4
A(
-
)
Y=
VARS
2nd F
√
—
GRAPH
+
–
Before
Starting
There may be differences in the results of calculations and graph plotting depending on the setting.
Return all settings to the default value and delete all data.
Set the zoom to the decimal window:
(
)
ENTER
A
ZOOM
7
ALPHA
Notes
Step & Key Operation
Display
2nd F
X/
/T/n
x
2