1. DRILL
Find the area and circumference of each circle in terms of (pi) with the given information for each circle.
Radius = 5 in.
Diameter = 14 ft.
Radius = ½ yd.
Radius = 3x & Diameter = 2x + 20

2. 12.1 Circles in The Coordinate Plane

3. X & Y Intercepts
X – Intercept: is where the graph crosses the x-axis and the value of y = 0.
Y-Intercept: is where the graph crosses the y-axis and the value of x = 0.
Ex: x2 + y2 = 36
Ex: (x + 2) 2 + (y – 1) 2 = 16

4. Deriving the Equation of a Circle

5. Equation of a Circle The center of a circle is given by (h, k)
The radius of a circle is given by r
The equation of a circle in standard form is
(x – h)2 + (y – k)2 = r2

6. Finding the Equation of a Circle
Circle A
The center is (16, 10)
The radius is
The equation is
(x – 16)2 + (y – 10)2 = 100

7. Finding the Equation of a Circle
Circle B The center is (4, 20) The radius is 10 The equation is (x – 4)2 + (y – 20)2 = 100

8. Finding the Equation of a Circle
Circle O
The center is (0, 0)
The radius is
The equation is
x 2 + y 2 = 144

9. Graphing Circles
(x – 3)2 + (y – 2)2 = 9
Center (3, 2)
Radius of 3

10. Graphing Circles
(x + 4)2 + (y – 1)2 = 25
Center (-4, 1)
Radius of 5

11. Graphing Circles
(x – 5)2 + y2 = 36
Center (5, 0)
Radius of 6

12. Writing Equations of Circles
Write the standard equation of the circle: Center (4, 7) Radius of 5 (x – 4)2 + (y – 7)2 = 25

13. Writing Equations of Circles
Write the standard equation of the circle: Center (-3, 8) Radius of 6 (x + 3)2 + (y – 8)2 = 36

14. Writing Equations of Circles
Write the standard equation of the circle: Center (2, -9) Radius of (x – 2)2 + (y + 9)2 = 11

15. Writing Equations of Circles
Write the standard equation of the circle: Center (0, 6) Radius of x 2 + (y – 6)2 = 7

16. Writing Equations of Circles
Write the standard equation of the circle: Center (-1.9, 8.7) Radius of 3 (x + 1.9)2 + (y – 8.7)2 = 9

17. Homework
Complete the Worksheet