In this section of MATHguide, you will learn a variety of terms that are associated with circles. Here are the topics within this page:

• Radius
• Chord
• Diameter
• Secant
• Tangent
• Point of Tangency
• Instructional Videos
• Interactive Quizzes
• Activities
• Related Lessons

    We will look at geometric objects related to circles. The first object is a radius.

• Radius: A radius of a circle is a segment that has one endpoint on the circle and the other endpoint at the center of the circle.

    A picture of a radius can be seen here.

    The next geometric object for us to examine is a chord.

• Chord: A chord of a circle is a segment that has both of its endpoints on the circle.

    A picture of a chord can be seen here.

    Our next geometric object is a diamter.

• Diameter: The diamter of a circle is a segment that has both of its endpoints on the circle and it passes throught the center of the circle.

    A diameter is the longest chord of a circle. A picture of a diameter can be seen here.

    Next on our list of geometric objects is a secant line.

• Secant: A secant is a line that passes through two points on a circle.

    A picture of a secant can be seen here.

    The next geometric object is one that has great significance within calculus. It is a tangent.

• Tangent: A tangent is a line that intersects a circle only once.

    A picture of a tangent can be seen here.

    The next geometric object is called the point of tangency.

• Point of Tangency: The point of tangency is a point where a tangent line intersects a circle.

    A picture of a point of tangency can be seen here.

    An interesting fact concerning point of tangencies is this: A radius drawn to a point of tangency is always perpendicular to the tangent line. This can be seen within the next diagram.

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    Here are related lessons to the circle terminology.

    esson: Central Angles
    esson: Inscribed Angles
    esson: Chord-Chord Relationships
    esson: Secant-Secant Relationships