A **circle** has a **center** and all
of the points on the circle
lie the same distance from
the center.

The
distance from a
point on the
circle to its center is
called the **radius** of the circle.

The **inside of a circle** is
the set of all points whose
distance from the
center is less than the
radius.

The **outside of a circle** is
the set of all points whose
distance from the
center is greater than the
radius.

The
distance from one side of
a circle through the
center to the other side is called the
**diameter** of the circle.

A
line is **tangent** to a
circle if it meets the
circle at exactly one
point.

A
line segment both of
whose endpoints are
both on a circle is called a **chord** of
the circle.

A **triangle** is a figure determined by
three points consisting of
the three line
segments joining the three
points. The three
points are called the three
**vertices**, and the
line segments between
the vertices are called the **sides** of the triangle.

A **right triangle** is a
triangle where two of the
sides are
perpendicular to each
other.

In a right
triangle, the side which is not
perpendicular to one
of the other sides is called the
**hypoteneuse**.

A **right angle** is formed by two
perpendicular lines.