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Lesson Plan #65
Date: Thursday February 26th, 2015
Class: Geometry
Topic: Equation of a circle.
Aim: How can we graph a circle given its equation?
Objectives:
1) Students will be able graph a circle given its equation
2) Students will be able to write the equation of a circle given information about the circle
HW # 65:
Page 526 Written Exercises
#’s 18, 24, 25, 26, 35
Do Now:
1) Graph point 0 at the origin.
2) Sketch the graph of all points that are 5 units away from the origin
(Try using a compass)
3) What kind of figure have you graphed?
PROCEDURE:
Write the Aim and Do Now
Get students working!
Take attendance
Give Back HW
Collect HW
Go over the Do Now
Assignment #1:
Given a circle with center (ℎ, 𝑘) and a point on the circle (𝑥, 𝑦), find the length of the radius.
Equation of a circle with center (𝒉, 𝒌) and radius 𝒓is given by:
(𝑥 − ℎ)2 + (𝑦 − 𝑘)2 = 𝑟 2
Online Interactive Activity:
http://montanamath.org/geogebra/circle/circle.html
Example #1:
Find the center and radius of the circle with the equation. Sketch the graph of the circle
(𝑥 + 3)2 + (𝑦 − 5)2 = 4
Exercise 1:
Find the center and radius of each circle. Sketch the graph.
A) (𝑥 − 2)2 + (𝑦 + 4)2 = 9
B) (𝑥 + 7)2 + (𝑦 + 3)2 = 25
C) 𝑥 2 + (𝑦 − 1)2 = 49
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Exercise #2:
Write an equation of a circle with the given center and radius
A) C(0,0); r = 9
B) C(-3,-8); r = 6
Exercise #3:
Exercise #4:
Exercise #5:
Exercise #6:
C) C(1,-2); r = √3
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Group Work:
4
5
If enough time:
1A) Find the center and radius of the circle given by the equation x   y  7   16 .
Center: (
,
), radius - _____
2
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1B) Demonstrate using the distance formula whether or not the point (4,4) is inside the circle or outside the circle.