1. A chord that goes through the center of a circle
diameter

2. Common external tangent
A line that is tangent to more than one circle but does not cross between the circles
Common external tangent

3. A segment from the center of a circle to any point on the circle
radius

4. A line that intersects a circle in two separate points.
secant

5. A line that intersects a circle in only one point
tangent

6. The point where a tangent intersects a circle
Point of tangency

7. Common internal tangent
A line that is tangent to more than one circle and crosses in between the two circles.
Common internal tangent

8. Externally tangent circles
Circle that intersect in only one point and have no other points in common
Externally tangent circles

9. Circles with the same center but differing radii
Concentric circles

10. Internally tangent circles
Circles that intersect in only one point with one circle inside of the other (sharing interior points)
Internally tangent circles

11. An angle whose vertex lies on the circle
Inscribed angle

12. An arc measuring less than 180°
Minor arc

13. An arc whose endpoints lie on a diameter of a circle
semicircle

14. Find x
110°
120° A B
AB is a diameter
X = 60°
X = 70°