Center Circle

Finding the Center of a Circle

Multiple Choice

What is CD?

• Chord

• Secant

• Tangent

• Line

The Perpendicular Bisector

• Draw a chord on the circle.

• Cut this in half!

• It needs to be PERPENDICULAR

• The perpendicular bisector runs through the center

• GeoGebra has a tool to do this for you.

Click on first point and then second point

Center?

Somewhere on the perpendicular bisector is the center.

Multiple Choice

How might you find the center?

• Construct a different perpendicular bisector

• Cut the bisector in half

• Guess

• The intersection of the chord and the perpendicular bisector

Make 2 Perpendicular Bisectors

If each chord's perpendicular bisector goes through the center...then any 2 will meet at the center.

Use the intersect tool in GeoGebra

Fill in the Blanks

Find AC. (Do not include units.)

Multiple Choice

What is the length of chord CD?

• 3

• 6

• 12

• 36

Multiple Choice

Line segment CD is 18 units. What is the length of ED?

• 18

• 24

• 9

• 36

Multiple Choice

What point is the center of the circle?

• L

• M

• I

• K

• F