1. Warm Up Find the unknown side lengths in each special right triangle.
1. a 30°-60°-90° triangle with hypotenuse 2 ft
2. a 45°-45°-90° triangle with leg length 4 in.
3. a 30°-60°-90° triangle with longer leg length 3m

2. Essential Question
What is a circle? What are the different parts of a circle?

3. Unit 3: Circles/ Volume
Section 1: Introduction to Circles

4. Standard(s):
MCC9-12.G.C.2
Identify and describe relationships among inscribed angles, radii, and chords. Include the relationship between central, inscribed, and circumscribed angles; inscribed angles on a diameter are right angles; the radius of a circle is perpendicular to the tangent where the radius intersects the circle.

5. As we go through this lesson
Fill in your graphic organizer
Write in your definitions under what is it
Write the notation under how do I write it
Label each item on the circle at the top of the page.

6. What is a circle
A circle is the set of all points in a plane that are the same distance from a given point, called the center of the circle. A circle is named by the symbol  and its center. How do I write it C

7. What is the center of the circle?
The center of a circle is a fixed point in space that is an equal distance from every point on the circle. How do I write it? Based on what the point is labeled C

8. What is the diameter of a circle?
The distance across a circle through the center is the diameter of the circle. How do I write it: Based on it’s endpoints EM

9. What Is the radius of a circle?
The radius is the distance from the center of a circle to a point on the circle. How do I write it? Based on the end points CD

10. What is a chord:
A chord is a segment whose endpoints are points on the circle How do I write it? Based on it’s end points AB, PF

11. What is a central angle?
A central angle of a circle is an angle whose sides are radii. How do I write it? ∠ ECD, ∠ DCM

12. What is a secant line?
A line that intersects a circle at two points is called a secant line. How do I write it? NP

13. What is a Tangent line
A tangent line of a circle is a line that intersects the circle in exactly one point. How do I write it? DT

14. What is the point of tangency?
The point of tangency is the point at which a tangent intersects a circle. Note: Perpendicular to the radius How do I write it? D

15. What is an arc?
An arc is an unbroken portion of a circle that lies between two points on the circle. How do I write it? AB measure in degrees

16. What is a minor arc?
Two points on a circle determine a minor arc and a major arc; the minor arc is the arc with the lesser measure. How do I write it? PF

17. What is a major arc?
Two points on a circle determine a minor arc and a major arc; the major arc is the arc with the greater measure.
How do I write it? PEF

18. What is a semi circle?
A semi circle is an arc whose endpoints form the endpoints of a diameter of the circle. How do I write it? EM

19. What is an inscribed angle?
An angle whose vertex is on a circle and whose sides contain chords of the circle is an inscribed angle.
How do I write it? ∠ NPF