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Tangent And Secant Lines

In this video, we are going to look at tangent and secant lines.

Tangent Line: Line that intersects the circle, but only at one spot.

Secant Line: Line that intersects the circle, but in two spots and continues through the circle.

If the center of the circle is the point O, and the point where the tangent touches the circle is the point A, then \overline{OA} is the radius. The angle that the radius forms with the tangent line is always a right angle.

Tangent And Secant Lines

Video-Lesson Transcript

In this lesson, we’ll take a look at tangent and secant lines.

A tangent line is a line that intersects with a circle in only one spot.

This line drawn intersects with a circle at only one point. So, this is a tangent line.

A secant, on the other hand, intersects in two spots.

This is an example of a secant line.

Remember, a chord also intersects in two spots. But a secant continues through.

The part of a secant inside the circle is a chord. But the entire line is a secant. It extends on both sides and out of the circle.

Something important about the tangent line has to do with the radius.

If we have a point in the middle of the circle called O and the point where the tangent line intersects with the circle is called A. Then, \overline{\rm OA} will be the radius.

The angle that this radius makes with the tangent line is always a 90^{\circ} angle.

Very important note:

Tangent lines create a right angle when a radius is drawn to the point of intersection.

Tangent line intersects in one spot while secant intersects in two spots.