# Names in Circles

Lesson

We've already looked at a couple of different features of a circle including the:

• circumference: the distance around the edge of the circle.
• diameter: the distance from one side of the circle to the other, passing through the centre.
• radius: the distance from the centre of the circle to the edge.

Now we a going to look at a couple of new parts of a circle. Let's start by checking out the picture below.

Now let's explain each of these features.

• Tangent: a line that intersects the circumference of a circle in exactly one point. A tangent is perpendicular to the radius from the point where the tangent touches the circle.
• Arc: part of the circumference of the circle.
• Chord: a line that goes from one point to another on the circle's circumference, without passing through the centre.
• Sector: a section of the circle defined by two lines from the centre to the circumference. It looks like a piece of pizza. However, there are different kinds of "slices." A minor sector has an angle at the centre of the circle of less than $180^\circ$180°. A major sector has an angle at the centre of the circle of more than $180^\circ$180°. There are are some special kinds of sectors:
• Semicircle: a sector made from half the area of a circle.
• Quadrant: a sector made from a quarter of the area of a circle.
• Segment: an area made from a chord and an arc of the circle. Each chord produces two segments: a major segment (the large shape) and the minor segment (the small shape, like the one shaded in the picture above).
• Secant: a line that touches and passes through two points on a circle's circumference.
• Cyclic quadrilateral: a four-sided shape whose four points touch the circumference of a circle.

#### Worked Examples

##### Question 1

Which of the following is a secant of the attached circle?

1. GH

A

JK

B

AB

C

OI

D

CD

E

EF

F

GH

A

JK

B

AB

C

OI

D

CD

E

EF

F

##### Question 2

Which of the shaded areas represent a segment of a circle? Choose all correct options.

1. $A$A

A

$B$B

B

$C$C

C

$D$D

D

$A$A

A

$B$B

B

$C$C

C

$D$D

D