A line that intersects a curve or circle at two points

Try this Drag either orange dot. The blue line will always remain a secant to the circle,
except that if the two points coincide, the secant becomes a
tangent.

The blue line in the figure above is called the "secant to the circle c".

As you move one of the points P,Q, the secant will change accordingly. If the two points coincide at the same point, the secant becomes a tangent, since it now touches the circle at just one point.

The line segment inside the circle between P and Q is called a chord.

As shown in the figure on the right, when two secants intersect at a point outside the circle, there is an interesting relationship between the line segments thus formed.

See Intersecting Secants Theorem for a detailed explanation.

- Circle definition
- Radius of a circle
- Diameter of a circle
- Circumference of a circle
- Parts of a circle (diagram)
- Semicircle definition
- Tangent
- Secant
- Chord
- Intersecting chords theorem
- Intersecting secant lengths theorem
- Intersecting secant angles theorem
- Area of a circle
- Concentric circles
- Annulus
- Area of an annulus
- Sector of a circle
- Area of a circle sector
- Segment of a circle
- Area of a circle segment (given central angle)
- Area of a circle segment (given segment height)

- Basic Equation of a Circle (Center at origin)
- General Equation of a Circle (Center anywhere)
- Parametric Equation of a Circle

- Arc
- Arc length
- Arc angle measure
- Adjacent arcs
- Major/minor arcs
- Intercepted Arc
- Sector of a circle
- Radius of an arc or segment, given height/width
- Sagitta - height of an arc or segment

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All rights reserved