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x - MathnMind
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Your Notes<br />
9.3 Graph and Write Equations<br />
of Circles<br />
Goal p Graph and write equations of circles.<br />
VOCABULARY<br />
Circle<br />
Center<br />
Radius<br />
STANDARD EQUATION OF A CIRCLE WITH CENTER AT<br />
THE ORIGIN<br />
The standard form of the equation of a circle with<br />
center at (0, 0) and radius r is as follows:<br />
x2 1 y2 5<br />
Example 1 Graph an equation of a circle<br />
Graph y 2 5 2x 2 1 16. Identify the radius of the circle.<br />
Solution<br />
1. Rewrite the equation y2 5 2x2 1 16 in standard form<br />
as .<br />
y<br />
2. Identify the center and radius.<br />
From the equation, the graph is<br />
a circle centered at the origin<br />
1<br />
with radius r 5 5 .<br />
1<br />
x<br />
3. Draw the circle. First plot several<br />
convenient points that are 4 units<br />
from the origin, such as (0, ),<br />
(4, ), (0, ), and (24, ). Then draw the circle<br />
that passes through the points.<br />
238 Lesson 9.3 Algebra 2 Notetaking Guide Copyright © Holt McDougal. All rights reserved.
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